Anyway yes, it's a mere matter of days.
Depends on the developer.
Legend of Heroes support on Steam was completely sporadic and undocumented, there were no patch notes ever, no official patch releases ever, it was being maintained by one person in some office somewhere (not exaggerating, this was actually happening) - who probably did her best, but that game's support is fucked.
Undocumented, yes. Sporadic, no. I've been a regular on that game's Steam forum since its release (I'm a major fan) and there have been times when there were daily updates, sometimes even more frequent. No updates as in posts announcing patches or changes notes, but frequent instances of Steam downloading updates for the game. Most folks including myself give the programmer some leeway since she's the company's only programmer and doesn't have the time to juggle multiple projects AND write patch notes and she's generally fairly quick to program fixes. But I've been keeping track of both versions and the GOG version was frequently lagging behind. In fact, the Steam version received an update to address a flickering issue in Windows 10 around the end of July. Latest patch here is from January. Not criticizing the company, just pointing this out.
Unepic's multiplayer mode was tied to a Steam service, it wasn't a thing to be just "patched in" like flipping a switch.
True, but that wasn't the only update that was lagging. Take a look at its forum on this site and notice there's at least one thread there asking when GOG's gonna get the update that Steam received already. (which didn't contain online changes, just offline tweaking) The developer replied in that thread that he was sending the update to GOG as he was typing his reply. Said reply was over two weeks after the opening post. It's an indy game, guy has a large workload. I'm not pointing fingers. Merely pointing out that there were delays in updating the version here.
Same for that other game.
Guacamelee's multiplayer is strictly local even on Steam. Nuff said.
Your problem is that you have some weird expectations towards developers and game developing in general. You seem to think that because some people are shit at organizing or simply don't have the manpower, that means you are in some way shape or form correct.
You're not, but you do come across as whiny and entitled - also you don't even seem to understand what is going on.
I'm not raging at the developers for not having the time to release GOG updates in tandem with Steam's. I'm not demanding or expecting that they do. My post isn't meant as an accusation towards the developers. I am, however, pointing out that for a myriad of reasons (manpower, juggling different versions, effort creating stand-alone patches) updates for GOG games are more sporadic than for their Steam versions. I've seen it happen, it's a thing, so I'm correct by pointing that out. No entitlement, just pointing out a phenomenon without throwing judgement around.
Don't get mad, I'm not attacking you personally.