Is rocket salad comparatively heftier? (8)

I believe the answer is:

stockier

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'comparatively heftier?' is the definition.
I can't tell whether this definition defines the answer.

'is rocket salad' is the wordplay.
'salad' indicates an anagram (salad can refer to a mixture).
'is'+'rocket'='isrocket'
'isrocket' is an anagram of 'STOCKIER'.

Can you help me to learn more?

(Other definitions for stockier that I've seen before include "more sturdy?" , "having more beef" , "squatter?" .)

I've seen this clue in the Irish Times.

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