So if the GM wants of course the gods can take away the cleric's powers and the patrons the warlock's powers. Though it probably would be the best to inform the player that this is how it works before they choose the class.
But the reason why this is more relevant to warlocks rather than clerics, paladins or druids, is that thematically the warlock/patron relationship has chances to be way more antagonistic than on the divine side. The divine caster might be expected to some degree uphold and follow the tenets of their deity, but that character probably is an adherent of that deity because they agree with those tenets, so a conflict is far more unlikely. Yes, there could be some crisis of faith narrative, but that is not the core theme of those classes.
The core narrative of warlock however is bargaining for power. What would you be willing to do for power? What (and who) would you sacrifice? And for such themes to work, the patron must ask things that test the limits of the character and they need to have real leverage.
And yeah, you don't need to play it that way, but that is the inspiration of the class. And if you don't want to do that, and just have the patron as some impersonal or immaterial power source that is no longer actively relevant, then that just makes the warlock a sorcerer.
By that logic, we should also just eliminate the Cleric, Paladin, and Druid. Just play a Sorcerer if you don't want to be constantly bothered by things actively trying to ruin your life!
Alternatively, we could accept that people have different understandings or appreciations of what the Warlock provides, and that difference actually does matter, even though not everyone wants to engage 1,000,000% full-bore with every possible implication of the original inspirations.
Like, I dunno about you, but I'm not super jazzed about being a servant of Big Chuck, even though that's precisely what the inspiration is for the Paladin class. (The
Palatine Knights--the "Paladins"--were the most prestigious knights under Charlemagne, and written about extensively centuries after their deaths in the Matter of France.) But I'm pretty hyped to play a knight-errant healer-champion-soldier righting wrongs in the name of one's god, despite that being
totally unlike what the Paladins did.
I could go on (clerics being
scribes, for instance), but I think the point is made: we interact with the class on many levels, and different people want different things out of it. It's perfectly reasonable to want to have just that little air of "bad boy mage", without being superduperultra excited to get screwed over the instant you put a toe out of line. 3e already taught us that with its divine magic rules and how
poorly they were received by most players, creating a power that the GM could in theory use but which they functionally never
would because doing so would be a
gross betrayal of most groups' social contracts--at which point,
what is the point if it's never going to be used?
And that's precisely why my advice above was about setting the tone
before any of the level-ups or power-gains were to be had--moreover, to put the leverage on by giving the player the feeling of being the one getting the "good" end of the deal when the truth is rather the reverse, but the Warlock simply cannot see how their short-sighted pursuit leads to long-term major gains for the forces of evil.
And if you wanted classes where they all had serious,
enforced built-in flavor, that ship sailed ages ago. The designers of 5e themselves admitted the Fighter was as bland as oatmeal, one of Mr. Mearls' personal regrets about 5e's design. Demanding that only certain classes get chained to their narrative implications, while others aren't....despite them being balanced with the assumption that everyone is getting to use their class as-written consistently? Yeah, not seeing that working well among many...if any...groups.
