I agree that Roglič has been better at TT if TT is at the beginning or at the middle of a GT race. One i guess only needs to take a look at his physique, and how it changes during a GT race, to understand on why. Having a stronger team, that should help in that regard a bit. And another thing, where he has much potential, to preserve more TT power is health. A crash, a cold, stomach issues, due to bad nutrition ... That just takes massive amount off effort, for the body, to heal. And until now Roglič basically hasn't done a GT, without involving much of that.
P.S. As for the Giro. I can understand, on why some are not happy about the TJV decision. TDF will likely get all the spotlight in 2020 season, but realistically Giro did a better job at providing an overall route.