Since it is implied that it is the tadpole that "leveldrained" all of your companions, i figured the same would apply to Gale. Don't really se why he would get a special treatment.
That's not the impression I'd got.
If we look at the companions:
- Shadowheart has been memory-wiped by Sharrans, that could explain why she doesn't recall how to use most of her powers if she was ever more powerful than she is now (which we don't know, though if she has some connection to Moonhaven then she might be significantly older than she looks and so it would make sense).
- Lae'zel is implied to be pretty young and experienced anyway,.
- Wyll is implied to have been a waste of space pre-Mizora, so with her captured and unable to help him he might have reverted to his pre-pact state. Or perhaps she withdrew her powers anyway after the falling out they'd had just prior to capture.
- Astarion has been kept as a lowly puppet of a master vampire for a couple of centuries. It's not clear if or how he'd have gained power in that time, and prior to that he was a magistrate which doesn't necessarily mean he was experienced in any particular class skills.
Which is not to say you’re not right, of course. There could easily be some clue that I’d missed! But at the very least I think it’s the case for every companion that there’s some other possible explanation for them being low level than the tadpole.
Astarion has been fed on rats and the like his entire undead life, and he flat out says that vampire lords wouldn't give up a servant for a rival, so it is very plausible that he's never really been much more powerful than he is now. His job seems to have been to seduce people to come see the master more than killing people, according to what he tells you.
Warlock Pacts are in a bit of a grey zone when it comes to withdrawal of powers. If the patron could do it that simply, why bother with the Pact? After all, if you can grant a Pact, shouldn't you be able to grant spells to Clerics? Much safer bet, since the withdrawal of Clerical powers is pretty well established and doesn't require you to personally invest in someone. Then there is things like the Great Old One Patron, where we have explicit flavor text in the Player's Handbook that the entity might not even be aware of you drawing upon their magic and knowledge, so you haven't really been "given" anything. You've taken it, intentionally or not.
My hypothesis is that Warlock Pacts aren't something that can be just taken back, nor does it work like the normal divine magic where you're granted spells. Rather, I think a plausible explanation is that you're given a tie to the source of power (the Hells in Wyll's case) and knowledge on how to channel that power. With Mizora captured and Wyll infected, his connection to the Hells is plausibly weakened, in part due to the Netherese (according to Auntie Ethel) magic tied up in these special tadpoles.
For our unconfirmed companions, Karlach and Minsc, we have some simple explanations too. Karlach says it herself; back in the Blood War, Zariel gave her what she needed to get the job done, but now she's back to relying on muscles and steel. And Minsc, I believe, has been petrified for 100 years between BG2 and now.
