Inept earl admitting baron initially more competent (5)
I believe the answer is:
Here is my best explanation:
'more competent' is the definition.
('able' can be similar in meaning to 'competent')
'inept earl admitting baron initially' is the subsidiary indication.
'inept' indicates an anagram.
'admitting' means one lot of letters goes inside another.
'initially' says to take the initial letters.
The initial letter of 'baron' is 'b'.
'earl' is an anagram of 'aler'.
'aler' enclosing 'b' is 'abler'.
(Other definitions for abler that I've seen before include "fitter", "More skilled", "More gifted or competent - maybe a seaman?", "More proficient", "More accomplished", "The better", "stronger", "Stronger", "More capable" and "More competent, perhaps like seaman".)