The brand of the tune shouldn't have any effect on the reliability of the CVT. Rumors have been stirring around that Cobb doesn't offer a Stage 2 power package for the 15-16 WRX with CVT because the trans cant handle the additional strain of an extra 30-40 WHP.
I have 2 fiends who are currently on the Cobb stage 1 on 2015 WRXs and the CVTs seem to be handling the additional strain just fine. They don't have trouble shifting with their paddles and leaving the ECU to handle the shift points seems to be fine as well.
Slow is Smooth > Smooth is Fast