To be honest, I do agree with you partially that is height is important, but that’s not only factor here. Obviously, a 6’4” guy with same skill set should do better than someone 6 inches shorter, no disconnect there.
But, here Musa is struggling and Shaheen isn’t (though, at the end he took two tailenders, after Aussies crossed 500 at Gabba - I believe, containment isn’t something you should look from your lead pacer), because their skill set is different. Musa is the latest product of the hype brigade in PAK cricket (I call it “Kambakht Talunt”... I’ll tell you the meaning some days) with unrealistic expectations- guy was born as 5-6 years old ... and possess a FC stats of 17 wickets at 38 with economy of 4. But, that doesn’t tell full story - 3 of his his 7 FC games were played last year, when PAK domestic wickets were mine fields and he took 12 wickets at 24. This year, on wickets more common to other parts of world, he has 5 wickets in 4 games at like 70 with an economy of 4.2 and SR of almost 100 ...... I guess you got the idea.
Had he been 6’4”, he would have definitely been better; but as good as Shaheen.... or other way, had Shaheen been 5’6”, would he had been as such like Musa - I highly doubt both.
This was a selection blunder, which didn’t sound well when I mentioned it - but, I guess, scratching the bottom of barrel is indeed hurting fingernails now.