Like anyone that plays the game for more than 5 hours can tell, there's many, many perks and variations that completely break a weapon and make it useless.
I get Shrike's idea that for there to be good weapons, there must be bad ones, but I think this goes way past roguelike design and veers straight into frustration. The main example I can think of is the Nemesis.
It's a rare weapon that's extremely expensive and is emblematic, but it's also a trap and you should probably never bother with it. There's at least two perks in the AM tech that make it completely trash, Barrage and Unstable Ammo. Getting any of these two perks completely bricks the weapon, and since it always gets two extra perks, the chance that a Nemesis you find is immediately trash is extremely high, I'd say 50%.
The result of this confusing design is that what should be an exciting find is actually just something you ignore most of the time, and it's just kind of lame in general. This doesn't apply just to the Nemesis, that's just the best example I can think of. Getting a Prototype Reverence(which is what, 30% of your Reverences?) also makes it extremely trash due to how "free" extra shot works. There's plenty more examples, I'm sure people can post them here.