i'd say henry's more of an arsonist. michael's reasonings for burning the building down were most definitely due to phone guy talking about why he SHOULDN'T do it so much which is where he got the idea from. henry on the other hand had so many choices on what he could have done, such as melting william or only burning him. but nope! he wanted to burn an entire building down. this fascination is also seen in the silver eyes trilogy, he beckoned jen to burn everything down in the suicide note he gave to her. i will say though, he was literally going insane before he died so it probably just amplified that.