%hp and true damage needs to be removed

%hp on its own is ok (usually done as magic or physical damage which means countering with MR or Armor)

True damage again on its own is fine as it is countered by building HP.

Combining the two %hp true damage is problematic imo as there is no way to counter it as it has no way counter it.

With that said its not impossible to beat this mechanic as a tank, just extremly unlikely.