Tactics which are quite similar to Fonline (with exception of more useful and complex environment) used %mods quite a lot.
It allowed some perks to be useful in all situations where they benefit, instead of being marginally low somewhere and extremely important elsewhere. Just look at how BRD is in F1/2/Fonline and in Tactics. IIRC tactics gives 10% damage per it's two ranks to ranged weapons, which makes it as useful to minigun as to rocket launcher. OFC that this kind of perk would need other perks that you would want instead, so it's not the only way to go (and this is still what is wrong with lifegiver, by the way), but it would at least be more than "get this if you want to use miniguns", which also translates "you need another character to play miniguns, even if you already have machinegunner".
Now you also have already mentioned pyromaniac, fast shot, bonus melee damage or living anatomy, not to mention there already are percentage mods :d.
