This is too much like WoW.
Enemies should be player-legal, with some special cases.
Give them turrets, traps, henchmen, robots to toughen up the final fights.
And drugs- maybe they have the "good drugs"- ones that work like in 2238 (can take 2 at a time, have the old effects, etc.).
Maybe those could be lootable. Probably end up as special treasures stashed away.
Boss with statted gear, good perks, drugs, henchmen and turrets and bots. Plus traps.
If more than 1 player the Boss gets a twin. Per extra player. ("Here's my brother Darryl, here's my Other brother Darryl", etc.)
So less HP would be accompanied by increased DPS.
Also bosses and friends would have many cookies, which they eat when enemy approach is triggered.
Maybe another Special Case is that bosses have no soft cap...
But still "player legal".