I really don't get this complaint. In all the other souls games, most of the weapon types have the same moveset basically. The only real difference is the look of the weapon and damage. In Dark Souls 3, the only real difference between the broadsword and Astora's straight sword are level requirements and base damage because they both basically have the same moveset.
In BB, not only are their stat requirements but each weapon has its own moveset that you can only get on that weapon making it truly unique. I think the weapons are the best thing about BB. There are no tiers (ie this weapon is better than than weapon) and they are all unique and different and offer a different playstyle so I really don't understand the "no build variety" argument from people. Yeah, you can't duel wield any two weapons in the game like in DS2 but you can't do that in Demons, DS1, or DS3 and all three games have multiple weapons you can use but most just use the "best weapons". Not a lot of people do mail breaker runs but you can do a run with every weapon in BB there are all viable and interesting in their own way.
Build variety isn't just weapon variety. It's the combination of stats, loadout and playstyle. There are enough materials to upgrade several weapons per playthrough, so I don't need to specialize that much.
aravuus talked about this a bit already. But yeah in Souls game the many options you have to create and customize your character loadout will affect playstyle a lot more,
and there are more possibilities because the magic system, ranged options, shields vs no shields, heavy armour vs light, etc. can create more combinations. You can be a nimble ninja, a defensive greatshield tank, a two-handing brute, a stealthy archer, pew-pew magic from a distance, or mix any of those things up (e.g. a defensive tank with a crossbow as ranged support, or a nimble ninja with some support magic/miracles, or a pew pew tanky mage, etc.). And all of those have the potential for a very different playing experience.
In Bloodborne it's always gonna be an agile shield-less melee fighter. The possible differences are limited to: slow and strong (str, e.g. transformed kirkhammer/Holy sword), quick and fast (skill, e.g. blades of mercy, saw cleaver), risk/reward (bloodtinge with the Chikage or Bloodletter), ranged support (bloodtinge with stronger guns or arcane spells), and... that's kind of it.
Also, I highly disagree that there are no tiers. I can't think of any reason to use the Amygdala Arm, Beast Cutter, Stake Driver, or Reiterpallasch, and especially none that I can see to use the Fist of Gratia, Ludwig's Rifle, Piercing Rifle. Rosmarinus also doesn't seem worth the materials to upgrade (esp. with how late you get it), and the Church Cannon and Rifle Spear are pretty mediocre too. I mean they can be kinda fun to use, and that can be reason enough, but for
tiers? There are clearly superior options over all of these weapons.
Why? The only thing that sometimes irritated me was that you couldn't switch gems, or runes for that matter, when you were outside of the dream.
Because there are no reasons to ever use any other type of blood gem other than regular damage-boosting ones. It'd be far more interesting if all the dmg-boosting ones weren't there and you could actually customize your weapons with properties like slow poison, quick poison, HP regen, or bonus vs beasts/Kin, etc. But literally all of those gems are useless, making it a very poorly balanced system.