@gutten_morgen That’s not the way it works.
For example the %Physical damage bonus to Grenado will boost it even if you convert flat Physical to something else, i.e. Cold.
+100% Physical listed in GrimTools on the skill increasing Grenado’s Cold damage.
In my opinion (educated guess) %Pierce does nothing even if you convert some part of Grenado damage to Pierce.
These parts even if converted are boosted by their respective %damage bonuses.
This is counter-intuitive but perhaps for the better because it makes %damage bonuses useful even if damage is converted to some exotic type. More info and tests here Mechanics Guide