Some popes were so merciful! (7)
I believe the answer is:
clement
This clue could be a double definition.
'some popes' is the first definition.
(I have seen 'Several popes' mean 'clement' so perhaps 'popes' could also mean 'clement')
'merciful' is the second definition.
(associated in meaning)
'were so' acts as a link.
I am not very happy about this link. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for clement that I've seen before include "gentle approach" , "Several popes" , "Fine" , "9, the chef and MP" , "- - Attlee (PM)" .)