Personally I'm an extremely heavy Flare Blitz user and think it's a great move. In my opinion things like the kill power of the move are completely secondary to the most important features of it which are the super armor and the mobility it offers. It can be used as a strong punishment device not just for scrubby rolls, but for a great deal of moves that would be otherwise unsafe to attack or go in on, such as projectiles and large disjointed hitboxes.
For example, if a (zero suit) samus shoots her gun, a (t)link throws a boomerang, a DHD throws a frisbee, a sonic does a hasty spin dash, a meta knight initiates a tornado, there's a warlock punch, a shield breaker, and so on and so on, they should almost always take a flare blitz for it. At least as far as I'm concerned. You don't have to care even one bit about projectiles or the hitboxes of the moves you're attacking or even your precise positionality beyond "will I get there in time?" because you'll just go straight through it all, and the answer to that question is usually yes if your reaction time is reasonable. It's a great tool for hard punishes of moves that'd ordinarily be less punishable or more risky to try and punish, as well as a tool for conditioning your opponents, making it an indispensable part of charizard's kit in my opinion.