Eh, I think you made a misstep in telling them to concede after seeing the Imperial Seal. You should have just played the game out from there, and just either excused yourself from the next game, or hold up the start of the next game until terms could be reached about what you and the table feel is appropriate.
As you're not playing for anything other than "fun", even a full deck of proxies would be fine in my eyes, so long as the person piloting the deck is paying attention to what the level of the table is and what people are expecting out of their game. Trying to force a cEDH tuned deck into a less powerful table is foolish, as is trying to force a jank deck at a cEDH table.
Proxying doesn't devalue effort. Cultivating a collection is something you do for your own sake, and your enjoyment of that shouldn't hinge on what anyone else is playing.
Sounds a bit like you're being a poor loser and a bit salty, but still seem unwilling to either sit down and have talk with the other people about what you see as appropriate or being unwilling to just get up and walk away if you know you're not going to get the sort of game you want.
Proxies are fine, especially if someone went to the effort of making actually nice looking proxies.
I don't much care for counterfeit cards, and actively avoid them myself as I don't want any fake card mixed in with my very real cards... one bad apple spoils the whole barrel, as they say.