Please look at this graph from Hockeyviz.
Here are the takeaways:
Andrew MacDonald Is Bad
He's bad with Shayne Gostisbehere, he's awful with Ivan Provorov, and he'd likely be even worse with Mark Streit or Michael Del Zotto. Perhaps being paired with Radko Gudas would drag MacDonald to an almost-respectable level, but that would mean Philly would have to waste its most effective defenseman to cover its least effective one. That's bad.
Here's hoping that the plan is to send MacDonald through waivers to the AHL as soon as he becomes the guy that we can expose to Vegas to meet the veteran requirement. I'd like to not use Brandon Manning as that guy, because...
Gostisbehere-Manning, Although They're Sheltered, Is A Good Pairing
They're most certainly used as the third pairing, and Ghost in particular is among the most heavily sheltered defensemen in the entire NHL. I mean look at the discrepancy here:
He plays with a third-pairing partner (Manning and MacDonald, mostly) and first- or second-line forwards. But the huge difference is the quality of opponents that he faces. He's the most sheltered of regular Flyers defensemen in terms of opposing defensemen, but it's almost comical how sheltered he is against opposing forwards.
Coach Dave Hakstol usually sticks Gudas, Provorov, MacDonald, and Del Zotto with the tough matchups. Obviously it's not an exact match because hockey is a fluid game, but those four generally face opponents that play upwards of 16 minutes per game. Streit and Manning are a bit below that, but their average opposing forward is just below 16 minutes.
Ghost is essentially on an entirely separate scale. He's playing against third- and fourth- liners, and (as you can see in that first viz above) he's feasting on them. I imagine the theory is Philly thinks their top six forwards can do damage offensively, and sheltering Ghost provides yet another potential way for the Flyers to generate scoring.
As for Manning, he's been right around the team average in terms of shot differential. He makes less than a million dollars per year, and he's exactly what you want from a third-pairing defenseman. He's cheap, he understands the system, he kills penalties, and if someone takes a run at your prized Calder Finalist young defenseman (soon to be defensemen), then Mandog will throw hands.
Gudas-Del Zotto Needs To Continue Being A Thing
This is a simple section. This pairing is Philadelphia's best current option. That's it.
Provorov Should Be Playing With Streit, Not With MacDonald
Here's another simple one, and I really don't understand why Hakstol seems to refuse to acknowledge it. Provorov is significantly more impactful when he's being complemented by Streit than he is when he's being dragged down to the bottom of the Manayunk Canal by MacDonald.
This seems so simple, and I really hope that Hakstol's commitment to MacDonald is merely lip service to get everyone to shut up about dumping MacDonald from the lineup. He can't possibly think that MacDonald is helping this team in the long run. I'm clinging to the "we need to expose someone for the expansion draft and I don't want it to be Manning" excuse because I don't know how the fuck else to explain it.
15-3, 32-9, and 53-23 Isn't A Bad Lineup On The Blueline
There are three capable NHL defensive pairings. The first two (and specifically the first one) have the ability to match up with any opposing lineup, and even the third one wouldn't worry me if they got stuck out against a group of skilled forwards. Unless, of course, they got stuck there with a trio of forwards (like, say, Bellemare-Vandevelde-Gordon) who stink. Then we are almost certainly going to see them flub an exit attempt and give up a one-timer to Alex Ovechkin from the faceoff circle.