My experience is that some advocates are much better than most advocates. The best lawyer I've had was a trainee barrister, standing in for a run-of-the-mill high-street solicitor, who couldn't show up. Presumably because she was a trainee, she did a really meticulous job for me, on what was a trivial offence: speeding. Few lawyers would put much effort into a speeding ticket.
She got me off; I was speeding, but I had been charged under the wrong section of the Road Traffic Act. "I humbly submit, your honour, that it would be quite wrong, your honour, for my client to be convicted of an offence he didn't commit, your honour".