Everyone involved in entertainment is superficial (7)
I believe the answer is:
shallow
'superficial' is the definition.
('shallow' can be similar in meaning to 'superficial')
'everyone involved in entertainment' is the wordplay.
'everyone' becomes 'all' (I've seen this before).
'involved in' indicates putting letters inside.
'entertainment' becomes 'show' (show is a kind of entertainment).
'all' placed within 'show' is 'SHALLOW'.
'is' is the link.
(Other definitions for shallow that I've seen before include "requiring no serious thought" , "Frivolous" , "Having little depth" , "flimsy" , "Not profound" .)