If they can't gain hp, and they have 50 hp, i don't care if they get 2000 maxHP because the highest hp they will have is 50 (going by the no hp gain idea).
If we really wanted it to make sense, then poisoned units should take poison damage at the start or end of the turn. Right now a poison file is really expensive without a lot of payback. The ork is really good, but has lv 6 rankup and does -1 lawtia every turn. Mushroom girl is good as well, but fits in a monster file a lot more than a poison file. Hierrat assassin has a strong open skill, but it is very costly, and I suggest removing the conditional use: lawtia lv 4 clause. Secondly, he is a very ineffective unit.
Lastly, unless you have grim retrieval, once you use breath of deaths you have almost no fighting power left (except the SS that does the same thing, but 1 lp).