Zombified Piglins are not aggressive despite the config calling for Pig Zombies to be always aggressive...

Afaik the PigZombie class still exists without deprecation, and there is no "Zombie Piglin" class so I assume that same class is what controls the piglins. So... if anger works differently then I guess it's a matter of finding out what that is...

The official namespace JE name for the new mob is zombified_piglin
https://minecraft.gamepedia.com/Zombified_Piglin

and the Bukkit API specifies
public static final EntityType ZOMBIFIED_PIGLIN
https://hub.spigotmc.org/javadocs/spigot/org/bukkit/entity/EntityType.html#ZOMBIFIED_PIGLIN

yes EntityType enum changed but there is no such class, so I assume it still uses the PigZombie class - and I have yet to receive any reports about an invalid cast.

Has aggression behavior changed? I don't remember reading anything about it so I assume no...

There is still a problem. Zombies piglins are not aggressive, although this feature is enabled in the plugin config.