Thanataphobia isn't a good perk on Legion anymore, and I want to put down the narrative that it is.
One single person healing nullifies 90% of the Perk's value, and most of the time you're much better off spending your time downing someone already injured than running around making sure everyone is injured.
Plus, by running around and stabbing everyone, you're applying mapwide pressure anyway, which is Thanatophobia's intended niche. It just sucks. If it worked the way it used to, it would be a lot better. One single person healing breaks the entire perk.
I prefer using perks that reward me for having good game sense. Thanataphobia is compelling you to avoid the injured guy you're chasing to activate its final stack instead, but by working to get full value out of the perk, you're potentially abandoning favorable chases.
The problem is that the numbers are just tuned way too low unless you get the fourth stack. It would be a different story if it was "serviceable" at two or three stacks, but it's extremely weak until four, where it actually becomes a perk. The time you spend making sure all four people are injured is better spent securing downs and hooks. One person healing (or being healed by someone) for only a few seconds isn't worth it, and the slowdown isn't worth it either since it's only 16 seconds at max stacks with a completely unworked gen (meaning most of the time it'll be less than an additional 16 seconds of slowdown since gens will normally have SOME progress already on them, unless you're using Corrupt Intervention)