Most variable in quality but having the most marks? (10)

'most variable in quality but having the most marks?' is the definition.
I can't judge whether this definition defines the answer.

'most variable in quality but having the' is the wordplay.
'most' means to remove the last letter.
'variable in quality' becomes 'streaky' (streaky can mean of unreliable quality).
'but' becomes 'ies' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'having' means one lot of letters go next to another.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'streaky' with its final letter taken off is 'streak'.
'streak'+'ies'+'t'='STREAKIEST'

Can you help me to learn more?