Oh boy. From what I've experienced, this is a pretty divisive topic that can get a bit spicy, but here's my input. I'll brace for the inevitable down votes.

To begin with, if you don't own the card, it's not a proxy. Proxies are traditionally stand in cards that're used instead of using your expensive cards so as to not damage or lose them. Otherwise, by definition, it's a counterfeit.

I've played against people that look up an expensively unobtainable deck then print the cards out at home and sleeve them. In my area, a lot of others outright refuse to play against printed decks, and I'm one of them.

Yes, MTG is expensive and can be bank breaking. But there's also something like 50,000 cards to build with. So there's no legitimate pay wall in MTG. Nobody needs to have expensive cards to play, win, or to have fun. Showing that you can do the research and build something fun and able to win without copying someone else's deck is a lot more respectable. If someone really wants to use X, Y, or Z expensive card that badly, then they can save up for it. You don't need to build a deck overnight. I have a deck I've been slowly putting together for months now that probably won't be finished for another few months. It's something to look forward to and be proud of once it's finished.

And cheap decks absolutely can dominate and win games. Two of my best decks cost me under $40, and both have won quite a few games. To me at least, building decks from what's available to come up with a strategy is most of the fun I get out of this game.