There absolutely is a power creep, but I don't think donks are THAT huge of a problem. Donks are a reality of the game. Since day 1 they've existed, and OP recognizes that, thus the format for Nats this year. Luck is a huge part of Pokemon, though. Deckbuilding and draw power help mediate the effects of luck on draw, and as far as flips in the game on "overpowered" Pokemon, like Gengar SF, those can be avoided through proper in-game strategy. The deck isn't just about dealing bench damage or "lol cheap prizes", it's about making the opponent adapt. That includes making them play around Fainting Spell. There are ways to do it, so just trying to run through Gengar and getting KOed in return isn't something to complain about. It's an avoidable risk that a player has to deal with. That isn't cheap. Machamp, an argument can be made for....but Machamp is becoming more and more a non-factor as the format evolves over time.
But back to the original point. Donks are something a player has to anticipate the possibility of and, through deck building, try to minimize the possibility of. Sometimes you just get a bad start. It happens to the best of us. They would be even harder to overcome without some of the trainers available to us. They increase the level of parity in the game. Some decks can get quick starts, but dedicated donk decks don't usually do too hot. The deck builder just needs to keep up with trends. Yes, there's a power creep. Yes, some decks set up very fast. Nothing is invincible, though. "Auto-decks" don't achieve real success against good players with decks tuned to the metagame.
"Parity" is the key word for the format right now, I think. There's a fairly level playing field. So much is playable, and the trainer engine that some have derided is a big part of that. "Set up" decks are only one class of many out there, and to try to shut out those that can deal damage early is NOT a way to "fix" anything. The key for decks that require heavy setup is the ability to weather the storm, then strike back and sweep. If your deck can't do that, then it needs work. Real simple.