Uh...I don't know if you mean Dark Souls but you're horribly misinformed if you think bosses don't scale with multiplayer in II. Because they do. As for enemies, they don't scale but again, this is by design so your original statement that the devs didn't want this, before you changed that statement anyway, is false.
And yes, some bosses are worse to fight with people than solo (Ancient Dragon, Fume Knight despite popular belief, Elana, Sinh, Alonne) unless you are a player that outright can't beat them solo. And co-op exists for those folks.
It sounds like you just don't like that the co-op heavy people play it differently from you. But this is getting off topic since we don't know how Bloodborne will compare to the previous games in this respect.
EDIT: Well, guess mobs do scale with summons also. Didn't know that, thanks for teaching me something new DealWithIt.