I don't think so. If I remember correctly, both parties (Bruce & Steve) have cited the story that Powerslave was a result of two separate song ideas that Steve suggested combining into one piece and Steve probably helped to "patch" the transitions and such together and his style and bass arrangement is, obviously, essential to the beautiful rhythmic section of the song. The guitarists probably had a big say in the solos too, but other than that, I think most of the elements can very well be from Bruce's pen, it's not like he's totally incapable with the musical theory, although lyrics and working with a virtuose guitarrist(s) are probably his strongest suit in general.
Disclaimer: I'm not on board with the
Bruce is so good at everything - a renaissance man par excellence! worship. I just think that while his certain capabilities & qualities get a fair share of overhype and whatever, people also tend to underestimate his songwriting/musical skills. He's not a virtuose player, that is for certain, but given how many great songs he has more or less contributed in, I don't think it's that surprising that he's essentially an alright songwriter too and sometimes hits a jackpot, with or without someone helping.