If we as a field determined that prostate brachytherapy is important and offers QOL or disease control benefits compared to VMAT or SBRT, it should be reflected in the training of radiation oncologists. If only we had some mechanism to ensure that residents got sufficient experience......
This is where you're off. Brachy doesn't offer any improvements in a real disease endpoint. For instance, look at the largest and best known prospective study: ASCENDE-RT. Absolutely no differens in mets at 9 years. Absolutely no difference in OS. Just an improvement in biochemical recurrence rates -- which unless leads to other improved endpoints -- is worthless in and of itself.
The one thing brachy does increase with certainty? Toxicity.
So I would argue it has not been determined "as a field" that this is neccessary. It is merely a niche modality with pluses and minuses.
As SABR develops further, and as local / regional salavage of truly isolated recurrences (as determined by PSMA) is further refined, the so called "advantages" of brachy will be less and less.
In my mind, given all that, it's perfectly reasonable to move it to the realm of fellowship. It's not a bread and butter technique for a reason.