[LeonB]

“Range” by David Epstein goes into this at length.

Studies about “mastery” that indicate you should stick to a single instrument tend to be about classical music where you’re playing (generously: ‘interpreting’) existing pieces, which is very easy to assess.

But qualitative research on successful creative musicians from a far broader range of genres demonstrates exactly what you’re saying: a range of experience in different instruments and genres is highly beneficial.