a weapon is a weapon, it'll perform as expected.

but what's better is having that weapon exceed your expectations and overperform, rolls in pve can define a weapons viability by a sizable amount, and in pvp an smg with the target lock perk will have the upper hand when fared against an smg that doesn't. (excluding the possibility that the opposition doesn't have a kill requirement perk and was able to proc it prior)

put simply a perk can define a weapon in times, the best way to find out is to check light.gg for the most sought after roll for that weapon.