i dont think Zda himself is overpowered, only his equip. His skill and DPS is normmal, the further you travel with better tier eqiupment you will see you dont need zda that much any more. In term of Supporter to control battlefield, his EQ can be replace with taunt ability of F'M and N'G. Interm of damage dealer Kassia and…
For first point, i think the "fusion" term here can refer to sacrifice, a trade off in order to gain better item at the end. So it should only be affected by input quality (item colour) not input index (damage, attribute), it's not like we're combining items to get a better one. We can consider runic is an item that lost…