Most raids require something for damage and something for add clear. Two good options are the ammit ar2 with incandescent for add clear and the taipan-4fr with triple tap/ firing line for damage. Both are craftable and their blueprints can be obtained by doing the mission from the relic condiut in the enclave area on savathun's throne world. Also some raids have champions (overload and unstoppable) so having something for that is also a good idea.

Null composure is love, life and the reason to play D2

Its funny when most of the weapons you get in a raid and you get it you will not use in that raid….

No gun is really essential but if you don't want elites on your team to cry because you're doing 10% less damage than them, firing line/triple tap linear fusions and snipers do the trick for damage, then literally anything that can kill ads is good too

Any good smg, a good linear, rocket with a clown cartridge (then you have 1 ghally in your team), xenophage, lament, divinity, arbalest. For add clearing I suggest Forbearence with chain reaction, or at least Salvager's salvo. For killing some tough enemies like ogres, knights, etc I suggest a shotgun with a trench barrel or any fusion rifle with a damage perk. That's probably it. Raids without contest mode can easily be done with a blue gear, so you don't even need God rolls in them.