I would equate the safety of standing on a Magical Express bus comparable to standing on a Disney Transport bus to the theme park.
As far as policy, training, and contracts go (or don't go), once in a blue moon overfull DME buses back to the airport have been with us ever since day one of DME.
I heartily disagree that, when it comes to getting guests back to the airport on time, Disney can say that if you are not satisfied with DME after following the instructions, then go find another way.
In terms of compensation, it would take about $100. cash to extend a typical vacation of a family of four by two days. Meanwhile, clerks not too high up can quickly throw out a single comp (non-upgradable) one day ticket which in some usage cases is worth over $100. and no heads upstairs would roll e.g. Disney neglecting to bring it up with Mears after the guest brought it up with Disney. I, personally, would prefer extra fast passes for compensation except that there are no ducats or other physical proof of holding such privilege when I arrive for my next vacation.