Reading doesn’t make you a better musician.
Musicianship is about so many things, only a few of which involve virtuosity as a sight reader. Plenty of things don’t require reading.
Sensitivity. Phrasing. Balance. Interpretation. Tuning. Line. Timbre. And on and on.
No, reading doesn’t make you a better musician. It makes you a faster musician.
It enables you to get from nowhere to musicality more quickly. So you can do more music, and spend more of your time on interpretation.
If we tell students that reading will make them better, they don’t really believe us. First, because they’ve seen and heard amazing musicians who can’t read, and second because they know that some of their skills don’t hinge on reading ability.
So tell them the truth: reading will make them faster musicians.