So battling against evil is like some never-ending game of whack-a-mole? It doesn't matter how hard the hero fights or how much they suffer or sacrifice, evil will just bounce back afresh forever and the combined efforts of all the Riders are ultimately completely futile?
Well that's depressing.
Depends on how you look at it, they keep fighting to avoid making previous efforts futile since most of the threats are new. There's this impression that Shocker and other organizations keep coming back, but in reality it's not all the monsters and commanders from that organization and mostly it's just taking a little bit from everything.
Also remember that at the end of every series the lead Rider (and some secondary ones some times) have
prevented a world-wide disaster by finishing their battle with whatever their show's villains are (except in 2 series). So, even if there's a new zodiarts appearing 5 years later, or the power source of the gaia memories themselves attacking, at least they're not doing so while the world is in flames.
And again, I have to reiterate, most of the threats they fight are the new ones. For example, I'll try not to get into spoilers, but the threat that Gaim and co. are facing has gone worlwide, so one can easily assume they're not going back to help Kouta because they're busy fighting somewhere else.
If we go by SPIRITS and the recent Kamen Rider Taisen, sometimes they don't even face superpowered threats but are helping mankind in some other way: whether it's by healing people, being a peace ambassador or preventing a war (and I mean a normal one with humans, as there are in the real world).
On that note, Kamen Rider SPIRITS presents the depressive scenario you're talking about since Badan brings back EVERYONE there. I'm talking about every single kaijin and commander the first 9 Riders had faced.
On the other hand, every supporting character is also back, and now there's a specialized team supporting the Riders with better technology than there was when first facing those villains. So, again, depends on how you look at it.
Do remember how there's this phrase that goes something like this: ''Kamen Rider is eternal''. They say that to imply that as long as evil is around somewhere, they'll be around too. This has been said over and over in many series.
I always got the impression that the shows are created essentially as standalone toy commercials series and then they just use a thin sprinkle of dialogue as a kind of plot duct tape to try and hold them all together
Not at all. The first 5 series were connected at all times. New Kamen Rider was initially stand alone but then got back to that previously established world from the first 5 series.
BLACK RX was a sequel that didn't need to give any kind of ''duct tape'' explanation.
This recent ''duct tape'' was used mostly in Decade since most of the series in the first Heisei decade (Kuuga-Kiva) were meant to be stand-alone. It has now changed in the Next Decade era, at least when it comes to the movies and the last episodes of each series.
It's simple, Toei is too fucking cheap to hire suit actors for it. I'm sure the Riders like Hongo and Gentarou ARE fighting Invess across the world, they just won't show it in-show because Toei is run by stingy fucks.
I'd like to believe it's more of a matter of screentime. They bothered to do it for episode 2 of Fourze.
