i remember Blaze to be INCREDIBLE and dish a bit of dmg while Healing himself, now that I play with him he feels nerfed…
i am at lvl 4 at him and still haven’t figured out a good build by now, his lvl 20 ability seems to lack options.
that, or everyone just got handed a manual on how to kill him ;(
Play 5 games or so on a champ and then complain about balance. Forums GG
He fell off after he received some minor nerfs. However, these nerfs mainly affected his mana pool and early solo-lane push power rather than his team fight abilities.
Bunker is still one of the best ultimates in the game - if you coordinate with your team and everybody is quick enough to react. Other than that, Blaze does not seem to fall outside the “medium” range. He is a “okay” bruiser and can be a decent off-tank with his slows, roots and even vision.
As to his 20 talents, the bunker upgrade is rather strong; again requiring people to actually use the oil spill to everyones advantage.
5 months since last time 
anyhow, did more matches and he seemed to gotten buffed, however i can’t recall the last time i fought a blitz and said “gosh, that bunker ability is annoying”
Look up “Combustioning for some free wins in low ranks.” by NotParadox on YouTube.
It will answer most of your questions