Sammy Hagar was a big solo band leader between Montrose & VH. The band was called Sammy Hagar. He was selling larger shows than Montrose and at the same level as VH.Haggar was in a band, Montrose.
And Nils Lofgren before joining the E Street Band was in the band Crazy Horse.
We are looking for solo artists (not guys who played in successful bands) who went from solo to a band. Bruno Mars, for example.
So he may not qualify as singer songwriter at the coffee shoppe.