I don't know about Fromsoft underestimating players, but I do feel like they had a major lack of effort in making enemies for the story mode, UNACs that is.
I mean, TE stacked HBPs. At least if their weapons were tuned (Which I imagine they aren't, at least for damage), they might be able to actually hurt the player with weapons.
I didn't have a remote idea of how to make a good AC when I started out on VD, so many of the AC fights were actually challenging. I even lost to that one LBP with the tiger emblem and rifle and sniper rifle. The game should've had a decent tutorial on assembling effective ACs, that way missions could've been more challenging without slaughtering newbies. That's my opinion anyway.