The output shafts are not "weak". But they do fail. I had one break at a lot less power and no transbrake. I did break a ring and pinion at some point in the years prior, that may have started the "crack".
I expect to break it in the near future, lol.
I ended up putting A&A input/ output shafts in mine. They get a twist in them through the lube holes right before they break. If your lube holes not round, but look more oval, you are just a few hits away from losing it.
