Stratton was technically both right and wrong timing at Maiden. Right in the sense that guitar talent is irrelevant, more than capable for the job, but wrong in a way cos they had a real rush of hiring a 2nd guitarist to record the first album, they didn't know him personally, and turns out chemistry wasn't perfect.
Two main reasons for why his stint lasted only some ten months or even less: 1) Too involved with the production of the first album, cardinal sin for the young Harris (now it wouldn't be a big deal) 2) Not willing to spend 24/7 with the rest of the lads. In defence of Stratton, I think thats a bs reason to kick someone out, don't think Harris personally liked him much. Now the relationship seems improved, good.
But, it is easier to find a good guitarist than a good singer. Bruce & Steve clashed a lot during the singers first year in Maiden, but Steve couldn't afford to give a boot so soon purely to creditibility reasons. I honestly think that had Bruce been a guitarist, his tenure would have lasted 2-3 years max. Bruce & Dennis have similar personalities.
Last but not least, Dennis was the one who recommended Clive. So he has a big part in the story of the GOAT band.