From my experience, most people have at least EV-trained their Pokemon and most of them use Ubers. All-legendary teams aren't THAT common, but yeah, they crop up quite a bit. I wouldn't say it's insanely high, but if you don't at least EV-train your Pokemon, you'll probably get your butt kicked, yeah. There are lots of people who are obviously just having fun though, I've battled any number of people who used level 40 Pokemon.