I have created a behaviour pack that lets the zombie aggro at a range of 15 blocks, the husk at 25 blocks, and the drowned at 35 blocks. While testing out the behaviors, I noticed that only a few of the mobs are actually targeting the vaild entity, rather than all of them. The code I am using for the husk is: 
"minecraft:behavior.nearest_attackable_target": {"priority": 2, "must_see": false, "reselect_targets": true, "within_radius": 25, "persist_time": 45, "entity_types": [{"filters": {"any_of": [

{ "test": "has_tag", "subject": "other", "operator": "equals", "value": "villain" }

]},"max_dist": 25}]},

And is the same for both the drowned and the zombie, albeit with different numbers (to get different ranges). The other thing I have done to their movement is disable random.stroll to make them only move when they find a valid target.
The amount of husk/drowned that target the vaild mob is completely random- sometimes one undead targets, other times 6 or 7 do.
The video attached to this report showcases the mob's behaviour issues, and I can post more information if needed.