Dragon breath with x str damage is fine, you can also cause his bash to do x str damage as well, and give him hellspawn armor buff. change his transformation ranged damage to hero, splash and you have an updated hero. as for pf
heavy weap,
plate armor
allows him to benefit from the str stats from heavy and plate armor.
Also keep in mind that most of these heroes have say fire breath, thats 2 updated abilities, just go back and change the stat multiplier based on str or agi.
Savior, Panda, Mountain king all have stomp so all those heroes have stat damage.
Hell spawn and spider queen have roar, so those 2 have updated skills, see what am saying dark?
Also the bash x str/agi abilities can be used as new abilities on heroes, eg savior and all other heroes who have bash.