You can't stop someone from drawing a fake Picasso. and that's probably a lot of people. Whether it's a good or bad copy doesn''t matter to most people. People are just going to think it's the same thing in some random gallery, with probably some minor details only true afficionados of Picasso can recognize.
In any case, the copy of Picasso is acceptable to most people.
But what I think fascinates people a lot is when you
start to get those
deviations of that original formula. And those derivatives/deviations away from the "way Picasso drew it" is something a lot of people seem to enjoy. Like this painting of Super Mario as a Picasso.
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Kind of the same thing with game genres, especially in FPS/3PS/2D beat em ups/fighting games.
Take for instance KOF and Street Fighter. KOF's base is definitely one of Street Fighters at first, with the only difference being the 3v3 Team format.
But as the series progressed, starting with '96, we get some land mark mechanics that defined the series and distinguished itself from its foundation; hops, rolls, blowback attacks, guard cancels, comboable grabs, OTGs, techs rolls, etc. It basically stopped being 3v3 Street Fighter and became something of its own, which a lot of people internationally have grown to appreciate.
I don't think derivative game design doesn't matter, especially with what games laid the foundation for certain genres. In fact derivatives, I will argue, are also important for the appreciation of what came before it/the genre itself. And a great derivative can open a gateway of new ideas for a genre as well.
I don't think I would have appreciated or enjoyed something like Spikeout if I didn't play Yakuza 0 first, especially when you start doing 1 cc/deathless runs and start learning how to deal with multiple enemies/do combos in both those games. Everything Yakuza 0 does builds off a very similar foundation combat wise to Spikeout when you look at how it plays fundamentally, with Yakuza adding more mechanics like heat actions and different enemy types to spice things up. The heat system is something unique to Yakuza that I don't see a lot of other 3d action games have and is core the series. But even then, Spikeout still has some of its own identity with how the Charge hold system works, the way you can "Super Attacks" interactions with certain enemies and the more "disciplined" approach the game is going for compared to Yakuza.
I think a derivative piece fails is when it doesn't have any identity of its own, and is simply copy-pasting what has worked previously instead of something that makes it worth playing. Which is why I believe something like Concord was going to fall along the way side eventually(apart from its atrocious character designs and god awful marketing), even if it was a financial success.
But also a bad derivative does this hidden "meta damage" being for the genre itself, to where people bring up the "it's just another shitty game of this type, this genre is dying" argument. Which is something people would definitely always seem to say when there's a major flop in a particular genre, but then REWIND on that statement as soon as something in that genre does well again. Marvel Rivals comes out and suddenly, wouldn't you know!? "Hero Shooters are saved!" As if a decent chunk of people weren't still playing Overwatch 2 by the time Rivals came out. Sure, not as big as a cultural phenomenon as the 1st, but still to this day has more active players playing it on Steam than the entire communities of Street Fighter 6 and Tekken 8 on Steam combined.
And I also feel that it really does matter a LOT now when talking about derivative game design in a genre, especially these days where people on the internet want to just dumpster fire anything and all relations to that thing for clout and money, with total disregard on how their actions/words affect an impressionable young audience/the general masses (looking at you, "gaming is dead" youtube/tiktok grifters).