The only reason Pressey is no longer on the team other than that rosters can't have more than 15 players is he couldn't hit his jump shots. It wasn't because he is shorter than usual for smaller players.
That problem doesn't exist with Isaiah. The only problem I have with Isaiah is sometimes, more often than I like, he charges into the paint and loses the ball. But then again, Isaiah Thomas is not a vet who's been around forever like Amir Johnson. Same as Kelly. These are developing, complex stories and not yes or no absolute questions.