I appreciate all the replies and discourse, thank you! Just finished running a morning game, nice to come back to see everyone's thoughts on the matter
I'm not a fan of taking away class features either- I've never found it necessary! But the framework, the guidelines, the
consequences are built in. For example I was running for some relatively new players, one of the PCs was an oath of devotion paladin; they helped a party member steal a magic cloak by lying to the owner. "Don't lie or cheat." That night they had a dream-visitation from their deity, a thematic scene where they were reminded of their oath.
The player asked if they could switch up deity and oath to Ancients after that

(answer was yes, I let players change things up in the first few levels as they're still getting a feel for the character/game/party needs n' dynamic)
Yeah the art patron thing is an excellent comparison. I suppose warlocks require extra work on everyone's part to create and lay down some expectations; it kind of sucks that nothing was provided or suggested? Imagine if each warlock patron had something akin to a paladin oath- not an
oath, but contract/pact examples. At least that'd be
something to work off of, to riff on!
To whoever was saying "it should be totally in the warlocks hands," I'd be fine a warlock player coming up with some terms n' such because it'd be
something, and I could curate it if necessary to be appropriate/fit things.
So yeah a lot of this comes down to basically sitting down with a warlock player at session 0 and hammering something out. A little web-searching has showed me that I'm not the first person to have these sorts of questions regarding the warlock, I'm sure some people out there have come up with some examples n' suggestions to inspire.