Would Vanquish be better without regenerating health?
Here’s a curveball answer: No.
You’d need to change a lot of things in addition to health to make it work without health regeneration. If you remove regenerating health and left the rest of the game as-is, it would not work, would not be playable. The reason for this is because the game is so lethal and enemy bullets are largely hitscan. If you remove regenerating health, then you won’t have enough health to survive the level, unless you’re extremely good at locking enemies down pre-emptively, which is a skill no one would be able to develop in a game like this unless they were doggedly persistent.
You cannot reliably avoid damage from enemy gunfire, you have no real defense against incoming damage, and the levels require you to move into harm’s way in order to progress. Despite Vanquish adding dodging, rocket boosting, and cigarettes, the game is still largely about intentionally absorbing damage in order to output damage to enemies, then healing your damage off before going another round. Enemies take damage permanently, unlike you, so you can whittle them down no matter what position you’re in or how bad it gets. Every enemy is designed to be able to kill you from full health.
Every enemy and level is designed under the assumption that the player has an infinite supply of healing items available to them everywhere. For this reason, even if you replaced the regenerating health system with health packs, players are likely to run out, or not be able to cross the gap to the next heal. It would generate a lot of random deaths for no good reason.
How could you make it work? One proposal I have is to treat hitscan weapons from enemies more like slow moving lasers, like the ones you avoid in DMC or other games. Imagine the player can see the target points where guns are being aimed at him, maybe the guns have actual laser targeting, and you need to avoid those as they close in on you. Going with more of a Nier-esque bullet hell route might also be viable, but not fit the theme as well.
The exact health system I’m unsure about. You could treat it like MGR, have a limited number of collectible healing powerups that are dropped from enemies/environment, maybe dark souls it up a little and require you to manually use them. So effectively you have what’s technically a longer health bar that has to be manually managed instead of infinite reservoirs of health waiting to be tapped into. I mean, this is what Ninja Gaiden did, and that was lethal as all hell.
I mean, if you were really careful and adjusted a lot of the game, yeah it could work and possibly be better, but as-is, it’s the best solution we have for the type of game Vanquish is.