75-76 Aluminum 833 4 speed Overdrive trans questions ?

I have two OD833 transmissions behind mildly upgraded 340 engines and have not had any problems with either of them. They are not bushed but came out of slant six 1980s pickup trucks. I am just running street tires so not a great deal of stress is applied and I have never powershifted into OD so no problems there. I do first and second gear burnouts all the time but not powershifting. My form is not as good as it used to be so I let off the gas when I shift these days. I am wondering why bushing the countershaft helps with strength. Is it just a larger surface area pushing against the aluminum because of the bushing. The shaft doesn't turn in the case so there's not rotational wear. Just wondering.