Bruce' issue isn't technique. He knows how to take care of his voice. He was forced to learn that after wrecking his voice in the 80's and spending large parts of the 90's to get the higher range of his vocals back.
His actual problem is pride. Personally, I've been saying for years that Maiden should tune down a step and I'm convinced that a good 95% of the audience won't notice or mind. Funnily enough, they
have transposed a song before: Lord Of The Flies. The original is in F# minor, while the Death On The Road version is a step below in E minor. For the wrong reason though: So that Bruce can hit a higher octave in the chorus lol
Having said that, let's go with the argument, that tuning down would change the songs too much. Then they really need to think about what songs make the setlist. A ton of the classics like The Trooper or HBTN are constantly around a B4, which is quite taxing, even for young people. If you wanna play those you need to find other songs that are easier to sing, not fill the setlist with a ton of difficult songs. The other thing they could do is change up a few melodies, go for the lower harmony for example. Bruce seems to have gone a bit in that direction, you can see how he approaches the chorus of Aces High on the current tour.
Bruce is a fantastic singer and can hit some impressive pitches. Unfortunately it feels like he's continuously trying to prove that he can still hit the pitches which leads to a worse over all performance that hurts the songs. I'm afraid he's too stubborn to change.