I've been checking out the champions challenge and I notice that the blazing champion can be shut down pretty easily compared to other champions by running until you find a water space or just spamming projectiles at it until it dies. Whenever I see fight a blazing champion, it's basically a regular enemy with an attack boost. I was thinking that they could get a minor speed or attack speed boost, so they could get some burning damage in before you can find the aforementioned water space.
They actually were nerfed in 2.2.0 along with projecting champions. Before that update projecting champions could attack you from any range and through any obstacle if they had vision on you and blazing champions spread their death flame cloud even over water which dealt very annoying unavoidable damage to you. Maybe they are too weak now? I don't know but old blazing champions were terrible