They aren't really good advises in my opinion, I'm sorry.
You can't really rush cutoff and flank MGs at the same time since the MG will cover the cutoff. Rushing cutoff doesn't mean nothing, DevM loves to rush cutoff but it has nothing to do with 99% the player rushing cutoff.
Then Ostheer infantry isn't weak at all. HmG42/Mortar/Sniper/Pzgren aren't weak at all and are the best of their own categories. Grenadiers are weaker than RM, which is different from being unilaterally weak. And the compensation comes from the other infantry support. Now many ppls prefer to go Ostruppen because it is easier early game, it allows you to swarm USF with more troops while Relic hasn't design anything in USF arsenal to counter it, but Grenadiers are still good at what they do.
The OP shouldn't be afraid to lose many games as USF at the beginning. USF isn't an easy faction to learn to play. As stated before, USF infantry is versatile but not specialized which is a weakness for those who don't master RM micro.
Rushing with RMs somewhere - in a blob usually - works to a certain extend. It stop working when you face better opponents.
If USF RM are good and resilient, that's not the case for their armor, being good with USF means knowing how to play with the M20, to deal damage, to keep it alive, even if the 222 has been buffed, the same goes for the Stuart, Sherman and Jackson.
If you can win a game without a M20 or a stuart, only by swarming RMs, this means you were already outskilling your opponent from the beginning.
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...
Ostheer and Sov are the get to start faction. Ostheer more than Sov because they provides you all the options to play along your tier progression. You start with pioneers + HMGs, then Grens + infantry support, then light/heavy armor counter + Pzgren, then medium tanks then heavy tanks. Can't be more simple.
Plus the fact you don't need to be aggressive, you simply try to respond what to your opponent does until you get stronger than him and reverse the battle.
OP: continue to play 1vs1, its the best place to improve, switch times to times USF and other factions to get different approach. You'll have progression phases with all Factions.
USF is hard to take in hands, then you understand how to blob, then you'll struggle vs people who know how to counter blobs, then you learn to flank, then you struggle vs people with good HMGs/Sniper micro, then you learn to use effectively your M20 or Stuart, then you face people who know how to deal with those then you get better etc...
Don't be afraid, the game is cool and worth the journey.