Sadly, bit so-so, these instrumentalists! (7)
I believe the answer is:
oboists
'these instrumentalists' is the definition.
(oboist is a kind of instrumentalist)
'sadly bit so-so' is the wordplay.
'sadly' indicates an anagram.
'bit'+'so'+'so'='bitsoso'
'bitsoso' with letters rearranged gives 'OBOISTS'.
(Other definitions for oboists that I've seen before include "10 across group" , "Woodwind players" , "Musicians" .)