Buffing the current functionality of Airbourne Assault is the wrong way to go imo. Luftwaffe Ground is already one of the stronger OKW doctrines strictly because of Falls and Valiant Assault. I'd rather see it changed into a less impactful Suppression loiter, made a little cheaper, and maintain the Fallschirmjäger reinforcement quirk as it's primary function so it's not a bait ability for people who don't understand that it's awfully useless.
221 I'd like to see either tried at 10F+15F for faster field presence, or 15F+10F for just faster lockdown conversion vs true Lights. That way your ROI from locking down Fuel would only take 8:20 to pay for itself instead of 10:00, and it'd be able to retire into being an Opal Blitz at a more reasonable timeframe and actually work as a way to generate a little extra income in the long term since it's impact is pretty much negligible right now.
People underestimate the 221 though, it's got some meat on it's bones and isn't terrible at bleeding. Problem is that it's not worth 30 Fuel more than a kubel since it just slows you down too much and you're often just better not building it at all.
Falls are a sidegrade of Obersoldaten with ambush mechanics, they are not a dealbreaker in the slightest, especially in a doctrine that lacks heavy tanks, artillery. The true reason the doctrine had relevancy was the smoke recon, which was and still is a godsend for 1vs1 OKW
The doctrine has already a powerful and versatile muni sink, so fixing another one wouldn't even buff it that much.
I don't see how that improves much of the 221, the 223 is absolutely not worth 25 or 30 fuel. The upgraded 223 is a MUCH WORSE M20 scout car that greatly lacks in dps The 221 armor and health stats match those of the Universal Carrier and WC51. Unless the timing can be lowered, the 221 shouldn't pay any extra fuel besides the 15 fuel cost. If the timing would make 223 too strong with a munition upgrade, then it should be enough to lock it behind first truck set up, but upgrading from 221 to 223 shouldn't delay your teching or cost further manpower, it just doesn't deserve it.
People don't "understimate" the 221, they rightfully ignore it because by performance/timing and performance/cost ratio it is by far one of the WORST light vehicles, arguably the worst, including all doctrinal vehicles