I think Fox is the level that Sexton can achieve. He might actually already be there....but there's a difference between doing it in 36 minutes and 25 minutes per game. If Sexton played 33+ minutes, kept his rate of production similar, and the Jazz have some success as a team I that would really spike his trade value. But he will probably always be seen as a guy who is a tougher fit unless he levels up his playmaking again.
This isn't a diss either. I think that if you put any of these boarderline all star guards on the market (Brunson, Fox, Trae, Garland, Murray etc) finding a good landing spot is easier said than done. So even if Sexton establishes himself among those guys, he's not going to be a fit for every team.