Hordes implies that Aribeth was redeemed but executed by Nasher to appease Neverwinter's vengeance-thirsty citizens, and the Hero of Neverwinter left the city in disgust. Under that canon, perhaps the Hero retired to Hilltop to study under a more altruistic and selfless master away from the fame and glory of their deeds in Neverwinter.
This would explain why your character is Drogan's best student despite there being no cause for it; because you're already a seasoned adventurer. This would also provide an explanation for the Contrasting Sequel Main Character dynamic between the two. After the events of the last game, your Hero put on a pair of Jade-Colored Glasses and developed a Deadpan Snarker Seen It All attitude. This also provides a hell of a character arc from the first game to the end of Hordes, where your character Jumps Off The Slippery Slope and becomes an Evil Overlord as a result of the psychological trauma and seeing their ideology broken down.
The one snag with this theory is how the characters from the base game don't recognize you in Hordes. However, it's implied a few years, perhaps several, pass between the two adventures. It's possible you've aged a bit and your old companions really don't recognize you, and you keep quiet about it. Additionally, between Hordes and Shadows of the Undrentide, your character goes on an adventure through the Plane of Shadow; it's possible the adventure physically changed your appearance.
Assuming the two are not happening at the same time as well, of course.
We know near to nothing about the protagonist of base game's past, except a rather generic description given depending on a race of choice. We also know that after the end of the game they cut off all ties with Nasher over the execution of Aribeth and are for that struck from Neverwinter records. The protagonist of Wyvern Crown was an adventurer who has come back home to support their family in the time of need. It is not impossible to imagine Hero of Neverwinter growing jaded with adventuring after Nasher's betrayal and deciding to hang up their sword (explaining where did all that gear go) and settle down on their parents' farm.
Since all of those are set in their own worlds that we know so little about, it is possible to Hand Wave any conflicting aspects of cosmologies. The only two who cannot be the same person are protagonists of Shadowguard and Kingmaker since the latter is said to have lost their parents as a baby and the former only at the verge of adulthood. But we know nothing about the past of Witch's Wake protagonist, except they had a title of a lord, were friends with a prince and trusted with hunting an evil witch. It is easy to imagine that the king is just another way to call emperor Rakka and the Shadowguard protagonist ended up with a high position in the empire and a friend to the Emperor's son after successfully hunting down the Crimson Prophet. Meanwhile, the protagonist of Kingmaker ends the game as a Lord of the Keep and there is a casual mention of a king in the game and they already are familiar with resurrection and being an object of interest of powerful entities like the Fey. it might even be that Night hag is another form of Kingmaker protagonist's grandmother.