Truly skilled trainers should TRY to win with their favorites.

Try.

Honestly, that's the most important part of the quote in my opinion. Karen isn't saying you're going to hit the top of the OU ladder with a team of NU pokemon (as if she would have any concept of "Smogon tiers"). She's just saying to be creative and try new tings. So many people are bashing the quote because a team comprised of your favorites will suck in OU or not do well in VGC. Who cares? I understand that many people have a competitive drive and want to win in these more organized, high-stakes formats, and that's fine. But if you never take the time to have some casual competitive fun with some of your favorite but under-powered pokemon, you're missing out on a lot of fun.

And I think a lot of people are interpreting it a bit too literally. Karen isn't saying that it's possible to win worlds with a Bidoof. She's saying that if everyone else is telling you that Bronzong is the best pokemon to fill a slot in your team, but you don't like Bronzong, you should have the boldness to replace it with a pokemon that you like more, even if people think you're stupid. Team weaknesses can (sometimes) be overcome with a bit of creativity, daring, and luck. And people should be applauded for taking these risks to use their preferred pokemon, not mocked for trying.