Tough but fair had always been the souls way. There are a bunch of DS3 bosses that I think are really counter intuitive (mostly aldritch and soul of cinder) from a souls perspective because they are super easy but have one or two moves that are crazy OP strong. Having faced them both 10+ times over various characters, builds and NG+s the fights amount to RNG.

A great example is Aldritches arrow rain move. Once he gets below 50% health it starts tracking you and follows you around - you need to unlock and run around the area until it stops. He also has giant fast moving souls spear spells (more like gwyndolin in DS1) that knock you over. Getting knocked over means while you are invulnerable and on the floor the arrows catch up and then you stand up into near instant death.

The issue is that there is literally no code to govern how often he does the arrow move. I have killed him without him using it once quite a few times, then I had one particularily frustrating attempt where he literally used it as soon as the last one expired for a total of 5 arrows rains. While I was running from guarenteed arrow rain death I couldn't damage the boss and it just becames him repeating the move until you eventually get frustrated make a mistake (in my case getting fed up and trying to kill him why he charged the 6th arrow attack only for it to fire and kill me when I was 2 quick hits from victory).

Likewise soul of cinder has a lot of stupid stuff (His multi swing, low telegraph, triple the range of all his other moves, unblockable, juggle lock move that will OHKO anyone below 30-35 Vig aside) the one that bothers me the most is actually his spear form in phase 1. He has a move where he charges briefly and then dashes forward very quickly and sweeps vertically up with his spear. This sends you flying into the air and then you end up flat on the floor. It doesn't hit as hard as the move above, but it is quite quick coming out. The frustrating part is that it dashes forward and then tracks incredibly well within a short distance around him. If he decides to use this mvoe multiple times in a row, the dash happens while you are still standing up,he is completely on top of you, and it will track and hit you mid roll as you roll to stand up.

I was a phantom with 50 Vig and FAP+2 etc for crazy high health. I watched him lock me in for 3 hits, the first catching me due to my own mistake and then him following up with the same move twice more catching me mid standing up. I died on the 3rd hit, and was treated to him using it another two times on the host (making it 5 consecutive uses) killing the host too.

I fought the boss maybe 15-20 times and I saw this 3 times. Each and every time it just felt unbelievably cheap and unfair. It made me genuinely dislike those two bosses despite me thinking the concept for the soul of cinder fight was great. Having victory and defeat depend on boss AI and RNG not only leads to infuriating deaths, but also cheapens the victories where you beat the boss without them really using their strongest moves. I have killed aldritch and seen him do nothing but the mass tiny soul arrows and short range easily avoided swings of his spear. Imagine if that was how he acted the first time a player faced this "Lord of Cinder - Devourer of the gods".

Consistency, balance and fairness is important. Having certain moves be really passive and others very aggressive only works with a boss AI that uses them correctly. Too much of either leads to bad player experiences. Sometimes the boss is completely passive and disappointingly easy, other times obnoxiously awkward.