I think that was the theory Mick Wall was trying to push, that the seeds for Bruce's discontent were sown during the recording of SIT. I'm not sure I buy it. With Adrian, we know he began to be unhappy at around this time and he said on the Maiden England DVD that it had a lot to do with the live performances. But I think what broke the camel's back for both had more to do with Steve single-handedly deciding to do a radical break with NPFTD. For Adrian that meant he had to leave. Bruce, I think, still had fun during the NPFTD cycle, but it might have dawned on him that when all was said and done, it was Steve who called the shots and that any creative development Bruce could experience was at Steve's mercy. And I think that after doing his own thing with Tattooed Millionaire, Bruce found it hard to get back to the Maiden corset. There were hints of this again in the mid-naughties, when Bruce indicated in interviews (I don't have links, don't ask me) that he was happier with the creative freedom he had with Tyranny of Souls than having to subordinate to Maiden.
I think before AMOLAD, Bruce and Steve had a talk about this and Steve agreed to give Bruce more freedom to express himself with Maiden. That would explain why a lot more songs and moments reminiscent of Bruce's solo albums started appearing on the Maiden albums, and also why Bruce lost interest in his solo career. Why would he want to make a solo album if Maiden let him put something like Empire of the Clouds on their album?