First off, why would it be a Duncan/Baynes pairing? Diaw should be the one starting during this Splitter injury. Baynes should be Duncan's backup, plain and simple, with Ayres backing up Boner or preferably off the team.
"Ayres is a silky kind of guy, blah blah blah"

. That's called running the offense. Any player can run up, set a screen for the ballhandler's guy and he'll end up wide open. Ayres can do it, Baynes can do it, Nando can do it, anyone. That's not being sneaky at all. And that small play is the only reason why Errors even sniffs the ball on offense, if he can catch it. I won't even bring up his defense because there's no point in bringing up that storm again.
And you hit the nail on the head about compe ion. Ayres' only "good" games came against the tiest compe ion in the league, against the Bucks and Jazz(not counting his defense against Davis). And the only reason Baynes hasn't been allowed to go against the starters is because Pop is an idiot when it comes to playing him. He's had maybe 3-5 games where he got solid minutes all game. The only way Ayres' stats even look good is because he's just tagging along while the rest of the teams carries his useless ass.
I guarantee if Baynes had been playing the whole season like Errors has, he would've been a solid backup to Tim and there'd be just about no debate about it, except for the people who cry about every little thing. So we're stuck with an undersized PF who can't create his own shot, can't dream of playing defense, and is only here because of our new braindead assistant coach... instead of a much needed backup SF to Kawhi.