If Maiden wanted better backing vocals, they could do it like they did with keyboards.
In fact, Colin Price, Dave's tech is a great singer. He sang Feed My Frankenstein with Alice Cooper when they opened for Maiden in 2011 (after Alice was chased offstage by the Frankenstein) and I actually saw him singing backing vocals when he was working as a tech with Nathalie Imbruglia in 2015.
They should have done it this year on HCW, because when H dropped out with BV's and Bruce started chatting with Edward, it was only Steve on oh oh oh's and it wasn't pretty.
But, they don't want to.