As far as I can tell, Soulgaze is an optional buy for sorcerers/wizards (YS, p. 174: "If you have the Sight, above, you may take Soulgaze for free if you so choose. It's not mandatory") ...
OK, my mistake; I thought both were "all wizards" non-optionally (I think the RPG may depart from DF-stories / WoJ canon on these ... ? ) .
Well, from a Doylist viewpoint, the narrative tension between the character's independent attitude and his ties to the Faerie Courts and Heaven/Hell is supposed to be part of his long-term arc and the source of various potential plot hooks, as well as the dichotomy between his drive for ever more magical power and his aspirations to freedom.
Fair enough!
Though I note that's a *LOT* of different powers in-play; IIRC not even Dresden himself had simultaneous access to Hellfire and Soulfire! I'd be Doylistically worried that all these heavy-duty obligations might result in MOST of his time being spent on the agendas & conflicts of those other Powers, and less on his own agendas & motivations.
... He expects to be able and pay access to these external power sources by doing the occasional favor or service to Faerie and Heaven/Hell. He plans to be their freelance agent every so often but never their permanent slave, which would be OK for his self-image and sense of honor. Those Powers help him, so it is good to do them a few favors once in a while, it is complete and lasting servitude he would object to. As it concerns potential conflicts between these various Powers' agendas and his own, or other obligations he may have, they shall be dealt with the best he can if and when they occur.
Faeries like those bargains, favor-for-service. Occasionally, it even works out well for the mortal involved... although the further up the Fae food-chain you go, the less likely it becomes that a bargain will seem like "a good idea" (or even "not a horrible idea") by the time you're done!
Pixies? A bargain a day keeps trouble at bay!
Faerie nobles? Oh CRAP, what did I do??!?
Heaven and Hell... mmmm... those get a bit less clear-cut.
The only "bargain" that Hell is interested in is the one that gets them your soul (or some sort of access to it, e.g. part of your True Name; or you doing (or permitting) something likely to tempt/corrupt you or another person), and as Burke noted
The only thing necessary for the triumph of evil is for good men to do nothing, so taking a "deal" to just do "nothing" can be effectively a complicit action.
Heaven... apparently doesn't MAKE that kind of bargain, or demand those kinds of services. They got that ineffable thing goin' on.
They apparently nudge the "right person for the job" in the direction of "a job that needs doing," and just MAYBE if they see you're doing a Good job (note the cap-G) you end up with Soulfire or some other sort of "reward". But -- being ineffable and all -- their Reward is one likely to be useful in other Heavenly endeavors and/or to end up doing Heaven's Work in other ways. They're ruddy bastards that way!