Demon's Souls is no saint here either, I mean do you all even remember? 5-1 is just ambush after ambush, several tiny rats ready to instantly plague you, guys hiding inside hay ready to run behind you on a bridge while 2 more are in front of you.
World 4 has infinite respawning invisible eye laser enemies in hordes that only go away if you kill their master, and then there are the roll happy skeletons with their best friends the sting ray assholes, which by the way the lock on does no favors for you here.
World 3 is mostly ok here, but there are also ambushes from prisoners, too, like 8 at a time.
World 2 has ambushes evetywhere. Tunnels filled with 10+ enemies, dogs and fat officials, flame lizard ambushes and so on.
World 1 same shit, I mean even the first boss is a horde of enemies attached to a boss.
Point is the whole series is like this, DS2 gets flak because it's easy to blame it on B-Team, or because they did a bait and switch with the lighting or whatever other nonsense excuse that makes it convienent to exclude the rest of the series.
A lot of it is that the DS2 fight mechanics are less forgiving. The roll has less iframes by default and the distance it travels is shorter. This means that the user has to be much more precise with their rolls to dodge things. Additionally, draining stamina on blocking causes the big stagger that makes people sad (though most single enemies and bosses never take advantage of that stagger, oddly).
On top of that, backstabs don't have 1 frame startups and vacuum properties, so they aren't as powerful and reliable. Also, you aren't completely invincible during a backstab.
Next up, enemies generally have higher poise in DS2, so you can't stun lock them as easily. Additionally, their windup on attacks is comparatively faster than it was on similarly placed enemies from DS1. There's also a greater variety of attacks by enemies and some that have odd timing and hit patterns (like the Heide Knight wrist flicks, or the Spider Hollow death pierce). Additionally, the poise characteristics appear a little different: in DS1, you could often hit an enemy while they were winding up and it would knock them out of the attack; in general, in DS2, even enemies with low poise will poise through an attack if they have started their windup. You have to hit them before they windup or deal enough damage to poise break them to knock them out of a windup (most notable on the standard samurai enemies in Iron Keep).
Finally, there are the hitboxes which are sometimes weird and a few times just bad. All the grabs are bad, the mimics are bad, and one or two other enemies aren't good either. The shockwave of the hammer ghouls throws people for a loop, for instance. This compounded with the lesser iframes and shorter rolls makes people grind their teeth at some encounters.
All in all, it builds up to a fight system that is a lot more stick-and-move and less able to be brute forced (by attacking first) and danced around within (by dodge rolling everything easily). The overall fight pattern of DS1 is a more refined Demon's, whereas DS2 seemed to put a lot of changes in place to specifically mess with players that had mastered DS1's fight system. Some felt it was less reliable (and in some cases it objectively is), but I feel it just changes it to something different.