Lack of powerful Arab rulers, we hear, is not much good? (2,5,6)
I believe the answer is:
no great shakes
'not much good?' is the definition.
(informal phrase meaning 'of poor quality')
'lack of powerful arab rulers we hear' is the wordplay.
'lack of' becomes 'no' (lack of money is no money).
'powerful' becomes 'great'.
'arab rulers' becomes 'sheiks'.
'we hear' shows a homophone (sound like).
'sheiks' sounds like 'shakes'.
'no'+'great'+'shakes'='NO GREAT SHAKES'
'is' acts as a link.
(Other definitions for no great shakes that I've seen before include "Of little merit" , "Minor tremors, perhaps" , "nothing to write home about" , "Small earthquake" , "unremarkable" .)