you can supergem but you need to do a proper order of combining gems. always “hold” the gem that adds to the powered up gem.
however the growth benefit of doing this starts to weaken rapidly. as in i get the strongest average possible grade 2 gem would only have a boost of 2 time damage overall, a max of +.5 firespeed and +.7 range while insanely increasing teh cost of duplicating the gem in future.
so no, just use amplifiers or push towards higher grade gems (unless it’s poison).