Consider playing a couple games where you swap decks. Commander players are used to downplaying their decks’ strengths and other decks’ weaknesses. Maybe you’re wrong and you just need to learn some strategy fundamentals, but it sounds likely that there really is a significant deck power disparity.
However, if that is the case, it’s possible that your deck’s shortcomings could be fixed without having to spend more than $5 on a single card. Adding more removal, removing duds, simplifying your game plan, or improving your mana base could help keep you in the game.
Oh also I would be derelict in my duties if I did not remind you that proxying cards is good and everyone should do it all the time. If your play group doesn’t allow proxies, they suck and you should start looking for some cool people to play with.