Even for fromsoft this is pretty bad. I don't remember having slowdowns and when killing a group of enemies in DeS, DS 1 & 2
Except that there was slowdown just in general throughout the games, whether you were doing anything or not.
DS2 in particular ran terribly on the PS3 which was low to mid 20s for the majority while on 360 the framerate was better but included screen tearing, which in my opinion is the ultimate no no if it happens frequently.
DS1 had several areas that ran terribly down in the teens no matter what was happening and general gameplay could often dip below 30 fps on both consoles.
Trying to remember back to Demon's Souls as it's been a long time since I've played and I can't really think of an instance of bad performance really, maybe the occassional dip here or there but I remember it running pretty solid and nothing like the Dark games, but of course, it also had a lot less going on graphically in comparison.
Bloodborne runs similarly to Demon's other than when other people are summoned in the game but it's odd as sometimes in BB I'll summon two people in and run through an area with zero framerate issues, other times I'll summon one guy in the same area and the framerate will fluctuate wildly for no apparent reason at all. Wondering if it has to do with latency or the connection between players.