Gale thinks he needs power to be worthy.
To be fair, a large part of Gale's thing was that he wanted power for power's sake.
His entire driving force is he wants to experience more of the weave. This eventually lead into him wanting to be more worthy, but the core is he just wants power.
That he on the one hand rejects Mizora and the things he has to do for her but on the other hand thinks he needs the infernal help to get things done, is a compelling conflict - same as Gale's is - just that it isn't very developed in his case and gets watered down even more if you don't kill Karlach.
This isn't the case actually.
Wyll
DOESN'T think he needs the infernal help to get things done. He needed it at the specific time he made the pact, but after that it wasn't necessary. Was it beneficial? Yes, the power allowed him to do more things, but was it necessary? No, he was a capable fighter before the pact (Since as a Noble he was tutored in martial combat).
Which is why this conflict isn't developed. Right in Act 1 he outright states he wants out of the pact, which wouldn't be the case if he thought he needed it.
He even gets upset in Act 2 when you do actually get to release him from his pact by saving Mizora in the Mindflayer Colony, only to be told that he won't truly be released from it for a length of time - If he felt that this infernal power was necessary, why would he be upset that he didn't lose it during one of the most important times of his life where he's facing down a cult that has an entire army at its disposal?
