And Steve's. And Rod's. The rest of the band - to a lesser extent, due to their limited creative control at that time.
Point is, Bruce (I think) is basically a tenor, and had spent years carefully and deliberately stretching his voice to enable him to get those high notes. Blaze, a baritone, being left with this very highly-pitched back catalogue to work with, was simply thrown in at the deep end. Hence his studio recordings are outstanding but when they went on the road and he started trying to sing Bruce-pitch songs night after night he struggled, and ended up with serious voice problems (he was lucky not to ruin his voice completely, forever). Bruce now claims he foresaw it and Janick eventually worked it out, but unfortunately by then it was too late.
What did they expect would happen? It looks rather like they hadn't really thought it through at all. If they had taken measures to accommodate Blaze's lower range (ie transposed the songs down a bit) could they have got a better performance from him? Based on the studio recordings and what we are seeing - and hearing - now, clearly yes. But they appear not to have realised this at the time - it simply "hadn't worked out" and they needed to do something drastic to get themselves back where they wanted to be.
To be honest, I'm starting to think Blaze was wasted on Maiden.