For the #1 threat the Magical Community, the Dark Dragon didn't really seem as threatening as he was made about to be since he was defeated thwarted fairly easily in all of his appearances. In the finale episode, Rose is even able to hold her own against him after he battles all the dragons. But it also occurred to me that he had the unique distinction of being the only dragon ever to go bad. The sheer danger of one of the most powerful magical creatures (and a protector creature) becoming evil and the psychological damage may have likely contributed to his perceived threat.
What's more, it may also count as The Corruption personified (or dragonfied) when one bears in mind he also convinced one of the Dragon Council to join the dark side.
In universe, it's explained as due to him being an Outside-Context Problem; since all dragons are Lawful Good in this universe, they've never had to develop the necessary skills to take one down if the need ever came up.
Then there's another piece of Fridge Brilliance: The Dark Dragon literally controls one of the other 13 greatest threats already, the #11, the Shade Demons.
The episode "Haley Gone Wild" becomes brilliant when you take two episodes into account: "Bite Father, Bite Son" and "Hero of the Hourglass". In the first episode, Lao Shi explains to Jake that the reason the Dragon council allowed Susan to marry the human Johnathan was because the latter apparently had a good heart. In the second episode, even though he can only go by the Huntsclan's perception on dragons being "monsters", Johnathan refuses to tell anything about dragons, because he loves Susan. Johnathan may not be aware of magic, but he has a strong moral compass considered valuable even amongst the Dragon Council. The brilliance comes in when one sees in the climax how exactly the Pooka's spell over Haley is broken. All it takes is Johnathan's tirade ("That show is a load of brainwashing, young lady!") to bring Haley back to her senses. In a way, that same moral compass saved the day.
Also take into note what we have seen of Jake's cousins: as this page notes below Jake at his worst is more mature than his relatives, and as Lao Shi hasn't been training Jake for that long, the difference probably began with 'the mortal' father who brought him up on manners and boundaries.
Fridge-Heartwarming: In the Season 1 finale, Rose still kept a picture of her and Jake from the dance he brought a Nyxx. While a good indication of how deeply she reciprocates Jake's affection, it's also food for thought why she loves him: bear in mind that was also the dance where her date Brad stood her up for another ("prettier") girl. And it doesn't help that she recently moved to that school, which almost made it an unhappy experience. Jake was the one who made her smile again when he wanted to dance with Rose instead. That was when she knew his feelings for her were unconditional.
It also explains why Brad is considered an Abhorrent Admirer. She remembers that it was him who dumped her for "the prettiest girl" at the dance. And one can imagine how annoying it is for Rose to deal with Brad repeatedly trying to sweep her off her feet when she remembers how shallow he was at the dance. He can pretend that breakup at the dance never happened, but Rose knows in her heart-of-hearts she'd rather have Jake for her boyfriend.
In "A Befuddled Mind", Spud succeeding where the other students failed at cracking the code becomes very symbolic. As he says, they're looking at the code in only one aspect (representing that their approach at being successful in life is one-dimensional). But to solve it, you need to look at the code "in 3-D" (meaning that Spud has a balanced, well-rounded life of being fun and smart).
Lao Shi often tries teaching Jake to (in his own words) "trust no one". Seems strange, given his role... Then you think about Chang (a dear friend, and possibly an intimate one), the majority of his family (Jake at his worst is more mature than any three of the relatives outside the immediate family, aside for Lao Shi himself), that thing about having had a fling with his own mortal enemy and it ending bad, and all the messes that his loyal friend Fu Dog does on a daily basis, and you realize he's perfectly justified in not fully trusting anyone.
Also, he's an incredibly stern teacher to Jake. Point is, Jake is theoretically responsible for all of the United States, and his only back up are Sun Park, who will eventually have to go back to Korea, his talented but inexperienced sister Haley, his arrogant, inexperienced and not-so-talented cousin Gregory, and Lao Shi himself, who is quite old and could end up crippled from old age or killed because he's not strong as he used to. Jake has an enormous responsibility, and Lao Shi is trying to make him capable of taking it before he can't help anymore... And apparently the much nicer teacher Sun Park reasons the same way, given the first thing she does when Jake got himself suspended in "Being Human" was to increase Haley's training many-fold and give her the doll of Madge the Motivational Unicorn.
Jake using Cupid's arrow on Rose when he believed she didn't love him anymore in "Love Cruise" seems evidence of Jake growing obsessed with her as Lao Shi believed. Then you remember he's permanently on the verge of a nervous breakdown and Rose's love was one of the few bright spots in his life, and you realize Jake was just scared beyond reason at the thought of losing her like he did in the Season 1 finale.
Leads to a dose of Fridge Horror. After Rose pulled her Heroic Sacrifice and nobody knew if he had succeeded in saving her, Jake flew away in anger, but the following morning he's almost calm, and just hoping she's alive and happy. What did he do that night?!
Why did Stacey fall for Spud at the end of the series? We see in "The Rotwood Files" that she's into sensitive Nice Guys, meaning that she likely started to like Spud after realizing how genuinely sweet he is.
In "Something Fishy This Way Comes" has this and a dose of Fridge Brilliance. The Kelpie has been stated to have been on the loose for a year, which is about the same time as Jake has been the american dragon at this point. The Mermaid City and officials might not have thought it a good match to pit a new inexperienced dragon against the #2 greatest threat to the magical community.
The horror sets in when you realise that the mermaid detectives didn't tell Lao Shi about it either, leaving plenty of time for the Kelpie to attack and devour several magical creatures. To hammer it home, the Kelpie transforms into a number of them during the episode, A troll, a dog and an elf. Those deaths are on your fins' mermaids!
Huntsboys 88 & 89 are all that's left of the Huntsclan after they were wiped out, and plan on continuing their work. That means in time, a new Huntsclan will be reborn.
In Dreamscape its revealed that Rotwood has a Chimera sealed in his subconsciousness, the #4 greatest threat to the magical community because of its powers in the dream realm, where it can cause horrifying nightmares afflicting an entire city. There might be an extra reason Rotwood is so mean.
This leads into a case of Fridge Brilliance and Fridge Irony: No mention is made of how the Chimera got into Rotwoods subconsciousness or how it was trapped there. It possible that Rotwood's sheer desire to catch a magical creature led to it being trapped in his mind, but without his knowledge.
So...small countries like Korea get their own dragons...but Jake is responsible for the ENTIRE United States? Aren't these dragon families ancient? Are they appointed by the UN or something? And were Jake's ancestors also responsible for the USA (Then why is grandpa still very "Chinese"?) or have they only gotten the duty for the last 2-3 generations? The dragons' biggest foe must be bureaucracy.
Jake is the first American Dragon and prior to him, there was a new boy on the block, the first Australian Dragon. So presumably not all countries have dragons, maybe only the Asian ones and until now there was no Dragon in charge of the USA. Also presumably being the American Dragon just means he's in charge of all dragons there since he does have relatives who are american dragons. In the future there'd probably be dozens of dragons in america with the one holding the title of American Dragon being the one selected to be in charge of them all.
In Breakout After Rose has knocked him out and has dragged him off to the huntsclan hideout, she holds Huntsmans hand as he wakes up. Its a small thing, but if she hadnt, he would have been more suspicious of her.