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
Greyhound