While I've been quite unimpressed with Rooker this season, he still has fewer than 200 MLB plate appearances with an overall 102 OPS+.
My biggest issue with Rooker is this roster and his glove but Miranda doesn't really fix that problem, either, because Josh Donaldson and Luis Arraez are occupying third base and Jorge Polanco is occupying second.
Before we christen Jose Miranda the second coming and Brent Rooker a waste of roster space, we should look at their numbers:
Brent Rooker AAA: 541 PAs, .932 OPS
Jose Miranda AAA: 285 PAs, .917 OPS
Obviously, Miranda is younger and has a position (though it's blocked in Minnesota) while Rooker is older and positionless but we need to temper our expectations and valuations of players just because we're frustrated with a different player in the moment. But a blocked position doesn't really help Miranda that much in the here and now. He's not 35 year old Josh Donaldson at third base, much less 23 year old Josh Donaldson at third base.
I expect Rooker will not be on the Twins 40-man next season and I'm pretty okay with that, though it's slightly risky. But I also understand why the front office is giving Rooker one more shot before kicking him (or another position player) off the 40-man roster to add Miranda for September.
Personally, I thought the time to call up Miranda was when Arraez was banged up and Donaldson wasn't playing third base but that window has passed.