No, the arsonists who die, die due to the mastermind. Sounds like you're quite an efficient one, thus your arsonist is fine. Having said that, he does aparantly have the lowest survivability, defencewise.
Deathdude, when you gonna fix your signature man? 
There is no sig problems 
And to be honest, i haven't teamed much, dont know how he copes on teams well.
Just remember, us Masterminds are proud of our supremacy over all, and in being superior, we must not affiliate ourselves with inferior archytypes.. unless target practising. 
Hey, it's cool, I often duo with other MMs as they watch in awe 
It's all up to your playstyle like a previous person said.
I had some problems with him dying in the past but since I adapted my playstyle, got me some shiny new macros for micro management I rarely loose a single minion.
I don't really have problems with my arsonist dying. I do, however, hear the woes of other thugs/ MMs that do. Now, I'm level 34 on him atm, casually blasting mishes on relentless, and I don't notice he dies much. He's using his big fire bomb attack thing and everything. I have my enforcers slotted for def, and I use darkest night when possible, but in all honesty I dont find him drawing agro that much. If a minion goes down ever, it might be him, but that rarely happens. Is this just me not taking advantage of him or something and missing out on damage/agro, or do other people find him okay?