I recently made a document breaking down beat em up enemy AI. While researching this I had a lot of thoughts.
The thing that I thought about the most is how different the design philosophy was in these games when compared to their modern day equivalents. Especially the philosophy expressed in the GDC talks covering God of War 2018's enemy design, which borrows a lot of beat 'em up dynamics.
Any player character or enemy has a set of natural limitations that stem from how their mechanics work - you can't do everything at once, neither can the enemies. These weaknesses don't stem from meters, cooldown timers, or any kind of "artificial" elements, they stem from the most basic fundamental rules of the games, hence they're natural.
Older games (generally speaking) tended to view these limitations not as a flaw to work around, but as a genuine weakness of the player which they can, and should capitalize on. In modern games, these limitations are seen as something like an inherently undesirable part of the games. They try to soften the blow as much as possible without outright removing those elements.
So when you apply that to enemy AI design, what you will see is enemies avoid attacking or stopping movement entirely when they're off-screen, picking position slots that are convenient for the player (usually in front of them rather than behind), even getting pushed into the screen as the player's attacking. On the player's side this is more variable, but you still see a tendency to add more lenient cancel windows, universal defensive mechanics, overpowered movement that lets you escape anything that would constitute a checkmate scenario, etc.
As a result, designers reduce the viable space in which they can challenge the player, often quite literally. The less of the player's weaknesses the enemies have to take advantage of (such as inability to hit multiple targets on opposite sides, limited FOV, recovery frames), the less they can rely on creating challenge through natural means. And the more they have to start relying on artificial, statistical means of doing this - super armor, meters, stamina, etc.
Or they could embrace the few remaining ways they have to challenge the player and emphasize those, which eventually homogenizes games, or emphasizes those elements to a point where they stop being particularly fun (such as testing reactions to randomized fast attack strings). What's more is, players get conditioned to expect friendlier & friendlier games, so the possibility space won't grow - it'll only keep shrinking.
I'd be surprised if developers don't feel the gamedev equivalent of suffocating claustrophobia when designing games this way.
