I honestly haven't seen an issue with healers yet. Cycao is correct - many DPSers try to be turrets without being the support as well. I think it's easy for people to get focused on someone as well, like that tank that just won't die even if they know he is getting leet healz.
Even on my GS/Sniper it is imperative to be tabbing on the other players as needed. Use your debuff, CC the guy not getting attacked, but about to attack, stay above and by pillars. These are just a few of the simplest tactics every GS/Sniper should use, but I see underused so often.