By all accounts, Karl-Anthony Towns had a great first year in New York. He was an offensive force, made the All-Star team, and was named to an All-NBA team. That said, he has his flaws, mainly on the defensive end. If the Knicks want to minimize those flaws, starting Mitchell Robinson alongside him may be the best option.
The Knicks ultimately made that lineup change last year in the Eastern Conference Finals, and lineups featuring Towns and Mitchell had a 108 defensive rating, which was better than with either of the Knicks' big men playing alone, or any lineup with neither of them on the floor.