Thus repeatedly less than brilliant (2-2)
I believe the answer is:
so-so
'less than brilliant' is the definition.
I can't judge whether this definition defines the answer.
'thus repeatedly' is the wordplay.
'thus' becomes 'so' (synonyms).
'repeatedly' shows that letters should be duplicated.
'so' doubled is 'SO-SO'.
Can you help me to learn more?
(Other definitions for so-so that I've seen before include "Of middling quality" , "Fair to middling" , "Informally, only moderately good or well" , "'Passable, middling (2-2)'" , "Rather middling" .)