In Thracia 776, lots of people complain that Eyvel is little more than a Jeigan despite her plot importance. However, in-story, there are several good reasons for her being that way. First she's a woman in her mid-to-late 30's, double the age of her adoptive kids; the only chara in her same age range before she gets Taken for Granite is Finn (Dagdar seems to be in his 40's). Second, Eyvel has been a local leader and Team Mom for several years, which surely put a damperon her fighting skills since she hasn't seemingly used them for a LONG while. Third, and most importantly: Eyvel is NOT a swordswoman, but actually an archer, therefore she isn't using the weapon she's most skilled at. Since she is Princess Briggid of Jungby but can't remember it (and the only person in the Thracia cast who can make the whole connection is Finn, but he likely only saw her as Briggid from afar since he returned to Leonster with Quan and Ethlyn a few years after she joined the group), Eyvel/Briggid has been in this situation for more than 12 years at the very least, and even worse, she doesn't have her best weapon (the Yewfelle bow, kept by Faval). Considering these points, it's next to no wonder that she Can't Catch Up in-plot. (Gameplay and Story Segregation explains the rest from the outside: if Eyvel was at full form andhad her Yewfelle, she'd be a borderline God-Mode Sue.)
There's a neat little example in the localized names provided by Fire Emblem Awakening: "Skasaher", the son of Ayra, has been completely renamed to "Ulster". Seems random at first, yes? Well, his name was intended to be "Scathach", as in the witch from Irish mythology. But not only does the kana not really get the name right, it's a Gender-Blender Name that could well offend people. So the solution? "Scathach" comes from the Ulster Cycle of tales, of course.
Leif seems to be relatively weak in Thracia, even if you compare him to other character of his level. And his promotion gains seem to be unfairly low compared to every other character in the game. And then you realize that his promoted class is named Prince, the same class that he started with in Genealogy. Of course his stats are low; he is basically a Trainee.
Dierdre is forbidden to meet men for fear that she will give birth to a kid with major Lopt blood. But the fact of her existence means that either she is the first one to be given this restriction, or people in her family just cannot avoid getting married despite sequestering themselves in the Spirit Forest for generations.
In the Oosawa manga, the elder of the group wasn't too happy to see her with Sigurd but accepted Dierdre's decision to leave. Perhaps she believed that it was Dierdre's destiny and she can't go against it, or that the other Lopt blood people had been extinguished after several generations of them being hunted down. (And indeed, Manfroy tells Arvis that the persecution against Lopts is still on, and that if people learned he had Lopt blood he'd be burned at the stake.)
Also it's likely that the former people of her lineage married persons that were from the Spirit Forest village and were guaranteed to not be Lopts; Manfroy took care to make sure that, for Julius to be born, two people with minor Lopt had kids. (Them being Dierdre and Arvis, obviously.) Dierdre's mom was a sort-of special case: Cigyun's hinted to have escaped from the Spirit Forest to see the outside world, which led to her marrying Viktor/having Arvis/being cheated on/cheating with Kurth/getting preggers with Dierdre/running back to the Forest when everything blew up in her face/giving birth to Dierdre and dying.