How do you try to integrate firearms (lasers) in a first-person RPG then?
You can't.
1. Make enemies bullet sponges. Then go by the "numbers go up" mantra, better weapons overcome the sponge faster. -- This sucks as system design.
Obviously shit design as you pointed out.
2. "The pseudo-simulationist approach". Make firearms very inaccurate, very prone to breaking, add wepon condition statistic, gamify the "time to iron sights", time to reload, weight in the inventory, the recoil, rounds fired per second, etc. Make firearms suck and gradually improve them through crafting/wepon modification, or through the player finding innately better weapons in the world. This way you can have weapons that always kill or cripple from 1-2 shots, but getting to actually hit something is the skill the player can build up.
Ton of problems with this system. First off, this feels like absolute shit. In a turn-based combat system such as Underrail/Dungeon Rats, your strategy/tactics are what make the combat feel fun. There is skill involved in how you approach certain encounters, and you can see the percentages for how successful your action will be. Where does the fun come from with this system? Oh shoot, I should have aimed at his head better? You did everything right but because of some arbitrary stat, you missed. It can also also make it so you need to play a certain way, such as rushing up close to all the enemies so your inaccuracy doesn't matter if you're unloading a shotgun or assault rifle magazine two inches from their chest.
Then there is the fact that the combat will feel like shit for the vast of the game until you're towards the end. If you get semi-accurate right around the middle of the game, the encounters will either be complete cakewalks or you will be reloading constantly playing against bots that auto target you with very high accuracy, essentially making it aim labs.
Plus, the enemies will be suffering from the same low health/high lethality gunplay you described, unless you yourself are a bullet sponge. No one wants to reload a long fight because an enemy got lucky and hit a shot they shouldn't have while you missed five in a row despite aiming dead center on the target, and if you can take bullets while the enemies can't, I have a hard time imaging how you will make encounters feel balanced. I can totally imagine an encounter that's supposed to be easy turning into a nightmare because you keep missing easy shots while the enemy hits all of theirs, while an encounter that's supposed to be climactic and difficult ends up very easy because you end up getting a lucky headshot.
Finally, there is the issue of immersion. In an isometric game, although you see your shots as hitting, you can't see where or how they land versus if you were in a first-person view. In Underrail, if an enemy takes a full SMG burst, I can assume their energy shield absorbed the blow, or that the shots grazed him, with only one or two getting absorbed by their bulletproof vest. In a first-person game, I can see where each of my bullets are supposed to land. I just shot three bullets into this guys skull, how is he alive? I just landed a shot on the arm that's holding his weapon, how does he hold onto it? Also lol at weapons randomly breaking. It always feels like shit. Just because I have never shot a gun in my life doesn't mean it should break halfway into my first magazine.
These are just a few of the issues that come at the top of my head, and I'm sure others or myself could think of more issues as well.
In the best case scenario, the combat will never be as good as your standard FPS shooter in terms of a gunplay feel, and it will never feel as tactical/interesting as a well executed turn-based combat system. It's trying to make a square peg fit into a round hole. Even if you get it in there, it's going to be fucked up on the other side.
