In a row with someone that defence and prosecution are held to the same evidential standards my understanding of a trial is a defence barrister does not have to "prove" anything, they have to provide a reasonable doubt, a prosecution barrister has to "prove" and provide evidence for things.A defence barrister can put forward a theory, a prosecution barrister has to put forward FACTS. They do not operate under the same burden of proof, because "proof" is not the job of a defence barrister, reasonable doubt it.That is the basis of the English legal system. You may not like that but there you go.I do not think the defence barrister breeched anything - because I have had the difference in requirements of the 2 explained to me fully, by the professionals I mentioned below including a therapist and a CPS Barrister.
So a defence barrister does not need "proof of theories", a prosecution barrister must prove their case.