Now the specific issue of OWB/biasing prosperity. First off, biasing prosperity does more than just add more colony games. It also gets you those cards more often, so I'd guess he knows them more than other people, better than other people, and that gives him a bit of an advantage. It also helps 2- and 3-card combos to hit more, which helps too; you recognize them, know how to play them, know their strengths. So like, I could bias intrigue all the time, and I'd know how to use the intrigue cards better, yadda yadda yadda yadda. So anyway, it inflates the winrate even when colonies aren't present.
Now, the idea that colonies don't make a big difference is pretty laughable to me. The idea that they just help the engine player is a little off, but largely right. The idea that they make games longer and that just helps the better player, well, that's pretty messed up. It promotes different things. It promotes a different style of gameplay. It promotes different strategies and combinations. Not always ones that are harder to do, not always does it reduce variance, not always does it help the stronger player. It just doesn't. I mean, platinum and colony have consistently consistently been in my bottom 5 win rate given availability cards for a very long time. Now, I guess this might just mean that I suck, and I get really lucky all the time in the non-colony games. But I don't think so. It's just a different skillset.
Ok, now for OWB-specific stuff. Even if we assume that the only difference is playing with colony and platinum, which as I point out above, isn't true, then let's look at these numbers. Pulling the data up today... He has 4393 games, overall winrate of 1.27. 2566 games with platinum and colony, winrate when those are available is 1.32. Okay, this means that there are 1827 games without platinum and colony, and his winrate in these games would be approximately (can't calculate exactly because of rounding) 1.20. If we scale that down to 19% (I can't tell what the exact percentage should be, because for some reason the availabilities for your basic cards aren't the same in the overall data), we'd get a winrate of 1.22. Which is a pretty big difference. I can't tell exactly how that affects his rating, but it's going to knock it back down a couple levels, at least, I expect. But as we all know, he's a top player anyway. Just not the clear #1 that the board makes it look like (unless you think that the current rating system take everything into account totally perfectly yadda yadda yadda see my last post).