In regards to ground crew earning $100k, if that's the case, that's a management issue of not having enough staff to cover the operation. Likewise if there is a group of pilot's earning $300k because of overtime (I don't know what they actually earn) that's a management issue. So if salaries are high because of overtime, the union should try to highlight it as an issue of bad management.
I'm outside of aviation now, but where I work there was a number of staff who weren't replaced but covered on overtime. It might be cheaper to start with than hiring a new employee, but now it's gone on for so long that it must be a cost. People are getting burnt out and while they may do overtime, they are taking sick days on their shifts, so there is even more overtime. If the staffing level was correct then there would be minmal overtime, as it would only be required to cover ad-hoc absences. Because of this I'm likely to earn an additional $18k-20k this year because of overtime and I don't do a lot of it.