It's very hard (I woud say outright impossible) to make a min-maxed charater that uses more than 2 different kinds of weapons (not counting grenades), let alone making it guns/melee hybrid. Reasons:
- only two weapon slots (+ utility slots for grenades) available, weapon switching in combat is possible but costly, even with Quick Pockets feat
- each weapon type requires spending feats to shine, you need to spend them wisely
I would suggest playing a character that uses just two different kinds of weapons and throws lots of grenades. Viable weapons for combinations:
- SMGs and ARs both have very AP effective starting 2 bursts attacks thanks to specialized Commando and Rapid Reloader, they also debuff enemies thanks to Suppresive Fire. ARs don't require much stats or feats
- Energy weapons have powerful crits and special attacks, using Aimed shot and Point shot with Smart Electroshock/Plasma pistol do wonders
- Sniper Rifles have Killing Spree for masacring large amount of enemies during first turn
- Pistols have Bullet Time for one turn of godmode, great special atatcks and ignore evasion at close range, but they are costly feat-wise
- Shotguns are good all-around weapon, nothing special for hybrids except for Kneecap Shot but they can be your backbone when cool stuff of other weapons is on cooldown
Now, I imagine Doomguy to be highly mobile tanking killing machine so I would pick Sprint and Hit and Run, they both ignore armor penalty (kind of) when used together so as long as you are killing things you will be able to move and kill more, even in full metal armor set.
Also, Grenadier and Three Pointer for making things go boom.
Example build (shotgun/AR) made on a knee:
https://underrail.info/build/?HggHBwoIAwPCoMKgAAAoAABQUDwoZGRQAGQAAAAAAHhkSkk7HsKwwpYVGTkWPmNOHwjCtUTioIoC4qGHBOKnqgPip7QD378(Added Yell for destealthing crawlers and more strength to wear supersteel armor)
