Because this strat is purely about snowballing and winning the game as fast as possible. Rifles and unit combinations are good if you plan to play properly. Pathfinder\airborn meta on the other hand is just plain and simple abuse.
I've watched video op gave, and the guy on the video summed it up pretty good. Basically he said that in order to have a chance to beat this strat, you just need to blob and concentrate your units as much as possible to kick the USF out before the Scotts hit the field, if you dont do this its over.
And as I was saying, path strats wont win you 30+ mins games, but if you allowed enemy to stay in the game using path strats you've failed at it. Premades on the video pretty much mastered this soy strat and games were literally already over for axis around 15 min mark.
On top of that, Airborn provides access to both AT gun\HMG so you are completely free to pick either LT\Cpt or delay them in favour of zooks. Not to mention that by paying 60 muni for support paradrop (AT gun), you save up to 53MP if you crew it with RE, 25MP with Pathfinders, 33MP with rifles, meaning that 4th reinforced model basically comes for free, plus paradrop allowing you to save huge amount of time via skipping building time and getting unit to the front line. It gives way too much flexibility, you see that enemy blobing? You drop 50cal. Enemy goes for LVs? You drop AT gun. Enemy is slacking behind, you dont drop anything and arm yourself with zooks.
And surely as a bonus airborn has access to one of the best Elite Inf in the game and has one of the strongest AT skillplane call-in.
In other words Paths+whole airborn tool kit allows you to just be on top of the enemy pretty much until early late game, if executed right, by the time serious threats hit the field game is basically over anyway.
As for paths performance main argument brought is JLI\Fallshims\PFs. But huge difference here is not even timing and resources required, its the Pop-cap. JLI\Fallshims cant be called at 1 min mark, you cant replace volks from the get go, meaning that even if you want to spam JLI\Fallshims you either have to kill off your volks to free your pop-cap, to be able to actually build something later or somehow play with very few volks squads.
PFs with G43 are cancer, but again you either mix them volks to stay somewhat competitive or you go full house PFs and give enemy an upper hand untill you mass G43s. In 3v3\4v4 they are more problematic, because of unit concentration.
In all honesty I think you are overplaying the power of USF Pathspam.
Yeah sure it's annoying and yeah sure it kinda works (the same way 2 sniper UKF might work) but let's be honest you are going against a faction that has Falls, Obers and flank locking FlakTrack. OST have assault support that instapins any blob for 125 munis and good luck getting your ambu out of there in time to support a regroup. Don't even get me started on Mortar timing, sniper counterplay, Flametrack counterplay.
It's a decent tactic that maybe sometimes plays out. But far far from gamebreaking or "too efficient". The same way Sturmtiger, a single shot casemate that has 40secs reload time, was "too OP". No, it's not.
They are an above average call in. Nothing more and nothing less.