Just tested this and can confirm. A Slayer melee attack doesn’t deal millions of damage anymore, it deals regular damage now (shared through TTB) and the enemy is killed by some other mechanic. I’m sure this is intentional, I mean they reprogrammed it in a way that it still kills the enemy without dealing more damage.
I always believed that how it worked previously was unintended because honestly it was a pretty brutal exploit.
However I can also confirm that Slayer killing an enemy doesn’t give you a second wind anymore. I believe what happens is that the code checks if an eligible target is struck by melee and just sets the enemy to “killed” after the act, and this doesn’t count as a player attack – hence no second wind. This actually looks like an unintended side effect to me.
edit: also just tested the interaction with overkill, and it’s as I expected. If the enemy has so little health that the regular melee damage kills them, you get overkill damage on your next shot because it’s your attack that kills them. If they had more health and Slayer kills it, you don’t get Overkill because something else in the code killed the enemy which doesn’t count as a player attack, just like with second winds.