Tbqh, the method described there isn't necessarily the "1 out of 20" teams either. Rather, the formula used, (1 - (0.5)^(1 / 20)), just means that Pokemon that are above the cutoff will, out of 20 random teams, have less than a 50% chance of not showing up at all. In practice, for a pokemon exactly on the OU cutoff, a 3.41% cutoff means that if you battle exactly 20 random teams a day, and if you play for D days, you'll run into the pokemon on an average D/2 days. However, that's not the same as the pokemon being in 1 out of 20 teams, and I'd argue that the current definition is LESS useful than the simplified 1/20 = 5%. The main difference is that, a 5% cutoff means that if you play against T random teams, you'll run into the pokemon on an average T/20 of those teams. That's a lot more direct and useful than the current definition, which only states that when you play against exactly 20, and only 20, teams, you have a 50% chance of running into the pokemon. The current definition also doesn't differentiate between if you run into the pokemon 1 time or 20 times during that 20 match streak, so while it can tell you you'll run into the pokemon 50% of your exactly-20-match-long runs, it doesn't even tell you how many pokemon you'll run into on average during those. I apologize if I didn't explain that well, but I think you know about probability well enough to get the gist of what I'm saying, and how a 5% (or 4% or 2.5% or w/e) cutoff would both be more meaningful and simpler than our current system.