While I do agree that the Smiths had a wonderful chemistry, as a drummer, I can tell you that what Mike Joyce brought to the band, another dozen drummers in England at the time could have done the same thing.
As for Andy, I think he is more unique, however for the entire time he was in the band, he was a junkie. I have been in a band with a junkie and known others - their number one priority is to get heroin, not the band, not their job, loved ones, etc. Johnny Marr helped hide Andy's heroin addiction from Morrissey for years. I would not be surprised in the least if he covered for Andy in the studio. It was in a live situation where Andy's playing couldn't hack it, he was found out and Morrissey chucked him out of the band. Andy dropped the lawsuit because he knew he owed Johnny and he needed immediate cash.
The "ideal scenario" of this perfect band is an illusion that was dreamt up by Morrissey and Marr. It was never a band of equals. For Mike to sue after the fact was a disgrace. He knew the deal was 10%. The rancor he stirred up between Moz and Marr made sure they never got back together again. Hope it was worth it.