Why not have a downgrade option that sets it so all weapons use ammo, including the low tier ones?
Also, I knew about the "hold button to load grenades", it's just that trying to quickly fire just one has some weird behaviour. The first shot should always be deadcenter, yet if you tap-fire, it'll fire once left, if you tap again it'll fire once right, and then if you tap once more it fires center. It also likes to sometimes just load 3-4 rockets and fire those even if I just quickly tap once. It's really finicky.
Actually, it'd be really nice to have a button to quickly switch upgrades on and off, cuz having to do that via the menu is a bit clunky.
Oh, and about that laser rifle upgrade, if I need to bother with being ammo efficient, then I'd just use the shotgun/assualt rifle, since, ya know, they don't use ammo. And the gauss shotty is already perfectly accurate AND it has a scope, so I don't ever need to bother with the laser rifle's upgrade, as it's rendered moot by the gauss shotgun being a scoped, infinite ammo weapon. The shotgun is also like the most common weapon in the entire game, so I'll pretty much always have it looooong before I can get my hands on a laser rifle. Also, it's upgrade is super cheap, I was playing doom2 with this and had the guass shotty by map03.
Soooo yeah, turns out that laser rifle upgrade ain't much of an upgrade.
That's also the problem of having infinite ammo weapons, any attempt to have something be ammo-efficient is immediately nullified by the simple fact that you can just switch to the infinite ammo weapon till you need the laser rifle/grenade launcher/Cannon again. Hell, the gauss shotty is good enough to take out anything that's an arachnotron or below, so I'd only ever be using the other weapons on bosses, barons, archviles, or hordes. Everything else you can just use the infinite ammo weapons on. After all, why waste ammo when you've got an infinite ammo weapon?