Material United Artists may argue lacks global appeal, missing their premieres (7)
I believe the answer is:
amalgam
'material united' is the definition.
(an amalgam is a mixture)
'artists may argue lacks global appeal missing their premieres' is the wordplay.
'their premieres' says to take the initial letters (premiere can mean the first or beginning).
The first letters of 'artists may argue lacks global appeal missing' is 'AMALGAM'.
(Other definitions for amalgam that I've seen before include "Alloy of mercury and another metal" , "Mixture - alloy of mercury" , "Mixture/blend" , "often filling" , "mix" .)