Yeah. That's actually something I'm worried about; that the higher Leagues (especially Platinum) are just too frustrating to play.
It is a bit frustrating and there is no incentive to play against yourself and other people in the platinum bracket.
An idea I had to possibly fix this: What if your level not only determined the deck you can submit but also your options when you go fight against the T500. So you might fight against triple mark decks but at least you have a triple mark of your own. This seems quite exciting as it would really add another dimension to PvE deckbuilding.
I was thinking the same thing, but instead you gained a skill point for every two levels, so you play a little handicapped.