[Kamen Rider Lucha]

I could almost support a reading of the "reset" that suggests it isn't literally what happens, but rather, it's Ren's fantasy of what happens after he dies/makes his wish -- or even, perhaps, a vision of some sort of afterlife.

But if we're going the literal route, which I do find more convincing...

I think the show painted the Rider War thing as a traumatic experience that broke everyone who participated. Like, pretty much the only development any of the "good" characters underwent was negative -- they struggled with succumbing to distrust, cynicism, and their baser natures. Freeing them of the curse of the Rider War allows their lives to revert to an undeniably better, more hopeful, and more virtuous status quo. A status quo they most certainly earned through seemingly endless physical and emotional torment... even if they don't remember it (although, the show seems to imply that they do remember their connections with each other, on some vague, instinctual/ephemeral, "why-do-I-feel-like-I-know-you?" sort of level).

Without the supernatural interference from Mirror World and the ensuing Rider War, actual nature can resume its course. Kitaoka will die of cancer, sure, but at least he'll go with dignity rather than with wish-fueled desperation. Asakura will remain safely behind bars for his crimes -- instead of breaking out, killing more people, and then committing suicide by cop -- as it always should have been. Shinji can live his carefree and happy-go-lucky life, and Ren can be with his girlfriend. The reset world is how things should be (and, actually, I don't necessarily see it as a happy ending -- it's a very neutral ending, in that, life will still go on for all of them, for better and worse. I mean, characters we've grown to love are doomed to die, or never become friends. That doesn't feel entirely happy to me).

I can see how one might think hitting the reset button invalidates the characters' experiences and makes the show a waste of time... but only if that person fails to understand the show's message. Namely, that The Rider War -- and war in general, probably -- is better off being deleted from the human experience, as it leads to nothing but irredeemable destruction and misery. The show wants to leave us with the notion that conflict for conflict's sake deserves to be erased from existence, and everyone is better off without it.

Maybe it would have been more satisfying if the writers had left the specifics to our imaginations and just faded to black, instead of giving us the details of the reset world. Personally, I don't know how the show fully articulates its themes without showing how the characters' lives are inarguably better without the influence of The Rider War. Obviously, YMMV.