IMO, the demotion penalty is one of the worst aspects of HBD. Teams can and do use AAA players to keep their ML teams fresh in real life. They will often call up a player for one game and then send him back down. The only restrictions on this in real life are the 10-day requirement and options.
The demotion penalties are not always just a few points:
Exhibit AThis guy lost 6 pts of glove, 4 in arm accuracy, 5 in vsl, 4 in vsr, 4 in eye, 5 in baserunning, 3 in power. Just a brutal penalty. To make matters worse, I demoted this guy before spring training started. I did it immediately following the rule 5 draft, but before the first ST game. Apparently, you need to demote them before the Rule 5 draft to avoid risk of a penalty.