The real problem is understanding that cap room is a limited commodity, Holmgren never got it, Hextall does. Players peak around 26-27 then slowly decline until their early 30s, and tend to fall off the cliff around age 33-34. So you never want contracts with big money in the "out" years, i.e., after age 32. So while McDonald is overpaid, if the young defensemen step up in 2-3 years, he has a movable contract since at 30 he'll be on a 3 year $15M contract in 2016-17, at which time that won't seem outrageous.
The problem with Hartnell's deal is twofold:
1) he's overpaid period, yeah, he's averaged 27g/56p the last three full seasons, but that was age 29-32, but that's all he can do, can't play on a checking line, can't play anything but wing, etc. And he's a horrible playoff performer, entire Flyer career, 72 games, 16g/41p, last 29 games, 4g/15p, and you don't pay big bucks to players who are MIA in April and May. And no, Holmgren isn't the only stupid GM out there, TB just signed Callahan, who'll turn 30 this season, to a 6 year, $34.8M deal. In his peak years, he's a 25g/50p forward - what about 3 years from now? Last 36 playoff games, 8g/15p.
2) He turns 33 this year on a 5 year deal, so he's nearing the career cliff with lot's of money left.
Umbarger is probably a 15g/30p 3rd/4th line winger the next two years before they buy him out. Hartnell is probably a 20g/40p player the next two years before he falls off the cliff and is basically a power play specialist who rarely sees the ice. Hartnell is the better player, but not that much better, and he'd be a huge cap albatross in 2 years.
The real issue is to avoid these contracts in the first place, they had to buy their way out of two of them, trade their way out of Hartnell, and now they're trying to figure out how to dump Vinny. When guys like Matt Read can come in and outproduce high priced veterans you can see the value in cultivating a pipeline of young, cheap talent.
Hextall needs to both take out the garbage, but also plant the victory garden.