[quote=@Voltus_Ventus]
<Snipped quote by Willy Vereb>

It's just a bit too OP.


[/quote]I can already think of several realistic drawbacks for them.
Being insensitive to pain sucks.
The poison may also destroy some of their ability to think which might be a mixed blessing because they would be pretty much unable to feel the taste of food or feel pleasure the normal way.
For the above these soldiers would require handlers to look over them outside combat and occasionally also solve issues on the battlefield.