I'm just going to start with by quickly repeating practically everyone else on this thread:
"Everyone has their own style, and ultimately base damage and crit range become decreasingly important as you advance levels so you can typically get away with whatever particular weapon you like." I mean, I have a high level warpriest with a few basic feat choices and a two-handed weapon who puts out +36 damage on a hit. That could be with a scythe on 2d4 or a greatsword on 2d6, and the extra 2 average damage per hit would barely be missed. [EDIT: I appreciate my warpriest wasn't the best choice of example because of sacred weapon, but you get my point.]
Following on from that, I GM a lot more than I play and for me that is where the sub-optimal options come into their own. I tend to expect a degree of optimisation from my players, or at least of not-actively-nerfing. That's fine. But as a GM I absolutely love having the flexibility to create thematically appropriate encounters from sub-par gear and builds, and explaining things as "NPCs with bad class/feat/gear choices do it."
I don't realistically expect any player to voluntarily wear shell armour (unless they found +5 shell armour of heavy fortification and fire immunity or something lying around, as someone pointed out earlier), but I would feel the game was diminished by not allowing me to put together an encounter of merfolk wearing it.
I'm quite lucky in that I don't play with many (any?) full-blown munchkins, but I've always been quietly pleased with the sub-par options for my own GMing needs.