You're on your first step to learn proper target priorization. The Scion is the sole reason of many groups failing against Collectors. Their AoE attacks can be devastating when the team is huddled together.
However it doesn't help much if you don't have the means to deal quickly with it. But in the meantime I suggest to try "dancing with the scion". Their slow speed means they are often paired or isolated (no troopers around). Trigger their melee so they stop firing and evade. Learn their attack pattern and try again to trigger their melee without getting slapped to death. This takes them effectively out of combat. With a melee Shadow it's incredibly fun and deadly for them, too.
Scions by themselves are not so much a problem. The real issue is the faction as a whole. Captains, troopers, abombs and swarms are an unthinkable pain. Sure scions and crabs are big bad meanies but they alone can be dealt with.
I actively avoid Collectors on PS3, not because I don't want to fight them, just 'cos of the memory leak. 50-50 it'll lock my PS3 up even in Silver.
Unlike many players here, I found the difficulty jumps from Bronze to Silver and Silver to Gold very noticeable and very difficult to deal with. I mention that here because I found that the jump from Bronze Collectors to Silver Collectors to be the hardest of the Silver jumps, but Silver Collectors to Gold Collectors less so.
Sometimes depending on the team even silver collectors can prove hard.