It seems you are too reliant on other "strong players". Those are indeed important, but im getting the feeling that you are waiting for players to down a boss. Every team (raid) needs a leader and i would recommend you to either assign a raidleader or raidlead yourself. And with leading i mean actually taking some time to explain tacts, letting people know if they are causing any mistakes and what is wiping the raid. Check recount, check who is taking unnecessary dmg. Players need the occasional slap in the face to wake up and perform 100%.