I used to make the turn from McKay onto South and then onto Center with a Prevost H345 all the time back in my charter days. And even take it down Henry and Elliot down to Ainslie sometimes. I never once rode a curb or took out a sign post. As for the turn on the route 58, GM New looks, Classics, D40LF (all generations-92,94 and 22) Orion 1 and 5 and 6 and 7 all have made that turn over the years. You have to turn wide or else you drive the bus into the yard of that one house after the turn.
I agree that some of the turns in the transit system are not ideal for buses, but as a professional driver you should be able to drive a bus without hitting or bumping anything.
If my memory serves me correctly, the Orion 1 buses almost never ran on the 58 anyway.