Last but not least, USF is difficult to play early game simply because its a being aggressive or losing faction. And it quite difficult to be aggressive when you simply don't known all the game mechanisms, the maps, the faction limits etc...
It's the easiest faction to play because they are the most basic faction lol. Their tech is so obviously linear... I dunno how you think it's difficult. Rifle spam into M20's, Stuarts and then get your tanks. It really isn't as complicated as you're making it out to be.
When it comes to Ostheer, they either go Osttruppen, hope the spam works or if it fails, they surrender. Unlike USF, if OST get any of their weapon's stolen... it's basically over for them. Be a MG stolen, be a Pak 40 stolen, be a Panzershreck stolen. It just creates more opportunities for USF. The fact that OST has such a heavy weapons team playstyle just opens up all kinds of vulnerabilities that USF doesn't have to worry about since most of the units USF use are just rifles, light vehicles into tanks.
When you play as OST, you need good map reads and weapon setups to stop those rifle squads. 1 wrong MG facing the wrong way or in the wrong area can cost you a game. That's not something you need to worry about with USF because all they do is spam rifles and run around with them. If you're relying on panzer grens to deal with rifles you're in big trouble already.