Ok as much as I don't like this site here's a good article but still to my point about overtraining in my personal view is not allowing your muscle fibers to properly heal so you can tear them down and regrow the problem is I think many people believe that tearing the muscle down frequently more than once a week sets you up going catabolic and then losing muscle so my question should have been if going high volume sets once per week make you go catabolic? Or does frequency make you go catabolic? Here's a good read at least they have some studies and not bro science.
From my understanding in this read they say frequency has been proven to increase hypertrophy and that overtraining is very unlikely for most people. One of the many reasons like most people I have gone to a 5 and 1 because doing a 3 day split is exhausting and not feasible for normal 90% of people so I can manage one muscle group a day with 20-30 sets without killing myself.
Your personal view was held for many years by the bodybuilding community.. Problem is there's never been a study to support the point to where a person would train too frequently to the point where they would actually lose muscle mass.. This is why Rodja was saying that overtraining is not a muscular issue.. However, you could train too frequently at a high enough intensity to decrease performance as a whole (what rodja was talking about with the CNS) which would in turn impact the amount of training volume you can accumulate over a given workout/week/ training cycle which would not be optimal for hypertrophy since volume is the most associated training variable with hypertrophy. Frequency doesn't make you go catabolic, according to studies protein synthesis returns to baseline around 36 hours after training that muscle. So, if anything we should be training muscles more frequently than we have traditionally for optimal gains in hypertrophy. Working with a high amount of volume once per week won't be catabolic either, it just wouldn't be as optimal as hitting a muscle group every few days as opposed to having 6 or 7 days off in between hitting that muscle again. If you don't enjoy training like this that is fine but if you're asking what is the best for hypertrophy then training with higher frequency and splitting up the volume is your answer.