I don't blame people for not liking Blaze/being critical of him and certainly objectively speaking his singing has some flaws as did his time with Maiden. But I am glad things went the way they did, and I can see why Maiden chose him. After the drama they went through with Bruce near the end, I can see why having someone they could get along with was important. And considering the dark chapter of Steve's life at the time, I get why Steve went with Blaze. He obviously saw potential there to help him create the dark mood of The X Factor. Not saying whether these were the objective right reasons or not (I am a fan of the Blaze era for what it's worth), I am just placing myself in the band's shoes.
I never saw Maiden live with Blaze so I can only comment on how good/bad he was by the recordings out there. Yes objectively there were some cringe worthy moments and the band didn't have as bright a future with him (for example the band would never be able to play Aces High or Seventh Son of a Seventh Son with him) as they have had and continue to have with Bruce (and Adrian). But the good part is (for those of us who enjoy them) we got The X Factor and Virtual XI which are damn good albums (minus a handful of flaws of course), Bruce and Adrian had awesome solo careers which produced incredible albums, after Blaze left he got to pursue a solo career and now the band is firing on all cylinders as a 6 piece.
Call it cheesy but I am thankful that Adrian and Bruce left, Blaze came in and then the reunion happened. I think everything happened for a reason. It all made and continues to make for some really incredible music and moments for us Maiden fans!