I was once a bus driver for Disney. I will say you learn quite a lot doing a job like that! It was probably the most stressful job I have had in my 10 years of working. A quick glance into the life of a WDW Bus Driver. OP wondered what the requirements were to drive a bus...actually quite simple. Have both arms and legs, be functioning, and pass the DOT test for certification for CDL Class B with P endorsement. There were 2 people in my training class that didn't pass, so not everyone can do it. Once you get out of training period, then it really gets crazy. You are now in charge of a 26,001 pound vehicle, with a max of about 60ish lives, not including your own, on a road, where there are people in rental cars, who have no idea where they are going. Have you ever seen someone cut across 2 lanes of traffic to make their exit on the highway? That has happened to me going to POP from MK, 45 mph, in the far right lane because we were only permitted the far right lane, or the 2nd lane from the right. That driver cut across then started to slow quickly...a very heavy bus, traveling 45 mph, has to try to slow down, without tossing 60ish people to the front windshield.
The drivers also have to keep an eye on the guests on the bus, I have had young teens use the hand rails as a jungle gym one day, was headed to MK. They refused to stop, I pulled of on world drive, called for a Manager, and the manager had a chat with them. They remained perfect the rest of the way.
Also have a few stories from working DS, taking highly intoxicated guests back to their resort...they don't like to sit still at all!
As for the long wait issue? Safety First, and always. What guests may not know is drivers are watched constantly. Not only are there cameras, there are managers doing audits on the roads, the black box on the dash (you have seen it) gives the driver their next dispatch, and is also the GPS, as it tracks the driver on a big map the dispatchers see.
All in all, just remember one thing. It isn't the drivers fault you waited 45 minutes, they get an assignment, wait for said bus to return to the park, do a changeover, and then start their route. Don't yell, scream or treat the drivers like dirt. They get plenty of that from management and upper management. Most actually love driving and being around all the guests.