If you do a WOWY 5v5 with Forbort & McNabb with Doughty, you will see that McNabb still keeps solid numbers when they are apart, whereas Drew's drop down to more average. Here are up to date numbers for this year:
McNabb with Doughty
CF60 69.87, CA60 34.62, CF% 66.9
GF60 1.89, GA60 0.63
McNabb without Doughty
CF60 65.82 CA60 51.04, CF% 56.3
GF60, 2.69, GA60 1.34
Doughty without McNabb
CF60 57.01 CA60 53.37, CF% 51.6
GF60, 2.53, GA60 2.05
Their numbers together are top notch. When they aren't together, McNabb plays better without Drew than Drew does without McNabb. Doughty puts up his best numbers with McNabb, and it's not even close. They have been stellar since put together last year, they allowed a single 5v5 goal this year in the 100ish minutes as linemates. They've played nearly 1200 minutes together since last season and have a CF% of 60.7 and a GF% of 59.7 since then, which is fantastic.
Forbort & Doughty
CF60 50.88, CA60 51.58, CF% 49.7
GF60 2.81, GA60 1.64
Forbort without Doughty
CF60 43.72 CA60 55.78, CF% 43.9
GF60, 1.51, GA60 2.51
Doughty without Forbort
CF60 69.75 CA 47.32, CF% 59.6
GF60, 1.91, GA60 1.91
Forbort and Doughty are not great together, they are an average pairing at best. One thing they do well is score, Doughty has picked it up offensively, but that's about it. Forbort's numbers are terrible without Doughty, there's no way around it. And that was against crap competition. Doughty's numbers jump substantially without Forbort. The only thing this pairing does well is scoring, and given their possession numbers that is absolutely going to drop off. They do not defend that well together and they do not control the play.
There really is no doubt that Forbort is getting carried on that line, which I am totally fine with. He's still learning the NHL game and is going to go through this kind of thing. There is also no doubt that McNabb is a superior linemate for Drew by far, and that he more than holds his own without him. I like Forbort, and I think he will be an asset to this team for a long time. He's going to grow and improve, but he's not near McNabb's level right now. Protecting Forbort and leaving McNabb exposed would be a terrible error.