I suppose it is not surprising that this is a topic, so here's my two cents of experience. Defeating opponents, finding glowies, etc. is what a team does. When I am on a small team with friends, if the glowies give xp or insp reward, we share them. If I am on a TF, it's usually about efficiency. That said, I agree that finding one's toon unable to do much is a drag. Rather like doorsitting in AE. While perhaps boring or disappointing, I prefer that to teams who cannot communicate and coordinate and/or that hopelessly wipe out, over and over. There exists a variety of playing styles. Being considerate is one of them. Tolerance for what might be called "cup of tea" preference differences is reasonable. [To be clear, the vast majority of CoH players are imho "considerate" and then some, often generous, heroic, etc.]
Often my blaster will see that the melee toons have engaged the bosses and/or EB, and either direct my blasts there and/or focus on defeating/clearing the surrounding mobs. E.g. in ITF, I try to take out the Cim surgeons first.
I had enough feedback and could see for myself when teamed with SGmates, that KB could be a genuine problem. With practice, the "death from above" technique (via fly, hover, jet pack) you either convert your KB to KD or at least reduce how much backwards force you are putting on a target. (For melee toons who may not understand, KB acts as a soft control, allowing me to apply yet more damage while taking none.)
Given that "kills" are shared when teamed, does it even matter whose what the final shot that defeated Romulus?
*A HAPPY MEMORY FROM JUSTICE SERVER*
I'll never forget speeding over and attacking full out - expecting to get one-shot KO'ed and admiring the floor - which got the AV's attention such that my teammate's scrapper was able to get it together to finish off the AV. To our mutual amazement, she said, "You saved me." (This was a top 20 SG on Justice that esteemed melee and often dismissive of "squishy" ATs.)