Check your privilege. You got 50 to 100% more an hour for working overtime BECAUSE it was a union shop. Yes the union that you resent for 'skimming' was getting you a way more than 10% bump in every paycheck.
If it wasn't a union shop, then you would have been working overtime at the same hourly rate as regular hours.
This is what GP objected to - if there's no incentive for management not to demand excessive overtime, they do it all the time and burn people out. If there are overtime limits or statutory pay increases for overtime, they manage their resources properly.