Grampy_Bone
Arcane
Dunno (if we talk about wiz8), by mid game my bard is usually second or third (if i have fighter and rogue) best melee attacker. A bit more vulnerable because of lower defenses, but dealing huge damage and being fast/agile too given that only basic stat for music you need to up is INT, which is usually at 100 by level 7 or smth, which means that you can start maxing STR/DEX/SPD asap. With ST it needs very little investment as two rings of traveler (or what were they called) bard gets instant whopping +40 ST. Bard's armor set although not best for juggernaut has very nice stat bonuses too. Give him Fang and he's maxed out on ST very early meaning that it's possible to max out DEX and SPD relatively early making him both strong as ox and fast/many attacks/initiative even earlier than fighter.2) Bards are a terrible melee class. No heavy armor OR stealth? Forget it. Ideally a bard should be playing music every round. If you really want a frontline bard, consider multiclassing to Ninja or Rogue after you get 18 Bard levels (Max needed to play all instruments). Its not recommended though.
I don't bother with much VIT for any of my characters ever but lizard fighters or similar 100% tanks. Nor bards or gadgeteers gain much from maxing it. Instruments/gadgets still take away stamina ridiculously fast making them useless and vulnerable if only using instruments/gadgets so in long fights i only bother to use insanity/haste/healing type of spells here and there, while going melee/guns 2/3ds of rounds. Guzzling stamina potions every second turn is just meh. Also omnigun isn't shit at all. It's only shit in early game and it's main problem is humongous weight of shooting stones. It's damage/status effect output summed with the fact that it's ranged weapon and can deal with elusive targets without spending a round for moving cannot be understated.
So the in best cast scenario a Bard is a third-rate fighter? That just proves my point. No Berserk, no backstab, no critical strike, bad armor, no stealth. You also admit that stamina loss from instruments makes the Bard too vulnerable for them to use Music often. So by your own description putting a Bard into melee range gives you an inferior combatant who is prevented from using their best talents. Weak. You might as well use any other hybrid fighter/caster who can at least use magic without knocking themselves out. Hell a melee Ranger would be better.
The omnigun has no damage bonus from Str so it's not even a contest. Any bow will outdamage it, the doubleshot crossbow, even the blunderbuss. Piddly 1% status effects do not make up for a 50-70% damage loss.