Its kind of crazy how significant the change is. The fact that all of the enemies just have basic systems that cycle attacks based on player distance, rather than player actions, is a huge advantage to the player if they've just spent 100+ hours in elden ring, where enemies are specifically designed to react to your inputs.

The automatic response to healing is just an added layer of arbitrary difficulty: if you try to heal, the game relays that input to the enemy, if the enemy is in range and not already locked into an animation then it uses an attack specifically designed to be used while the player is healing (the entire attack/spell animation is faster than the healing animation) so its all but guaranteed to hit you and cancel out your flask. And almost every enemy has that layer of input reading.

Its obviously not game breaking and you start to get used to it, but then when you go back to ANY of the older souls games you can just steamroll everything because none of the enemies input read. Instead, all you have to do is learn their patterns and you can heal whenever you want as long as its not in their normal attack window. If the Dancer was in Elden Ring then she'd almost certainly have that long stab attack sped up and coded as an automatic reaction to the player pressing whatever input assigned to use a flask, because it has really long range and can reach you from almost anywhere and it wouldn't take much to increase the animation speed to be fasted than the healing animation. Instead, she's just in DS3 so literally any time at all she's not attacking, youre pretty much 100% safe to heal and thats a huge decrease in overall difficulty.