@elubas: Look, I think we're 95% in agreement. I'm not talking about style, I'm talking about relative strengths. There are a lot of reasons why we might believe that such distortions are common. I mean, look at the tournament table for any club tournament, and compare it to a GM tournament table. It probably jumps out that GMs draw a lot, whereas club games are almost always decisive. You don't think that the positive correlation between draw rate and strength is going to impact rating? Of course it will (it may have a fairly substantial effect in the 1900-2200 range, where there seems to be a big uptick in the ratio of draws to decisive games).
I'd also point to guys like Morozevich, Aronian (in his earlier years), and Shirov, who'd gain tons of rating points whenever they entered a tournament with mainly 2500-2650 guys, but then lose them when they played Linares. Also, it seems very plausible that if Kramnik or Anand played 2500-2650 range tournaments, they might lose points due to their relatively high rate of draws. They're super solid, so I doubt they'd ever lose, but they just don't play a style that wins often enough to gain points.
Okay, that's just a handful of cases (which are speculative anyway), but to compound my sins with some anecdotal evidence, I find that I perform exceedingly well against inferior opponents. I'm rated about 1750 OTB, but I practically never lose to opponents rated 1550 -- I certainly don't draw half or lose 25% of my games with them. I win 95% of them.
But I often have trouble with opponents rated 1650-1750, and I do okay (about 50%) against opponents rated 1750-1850. I never win against opponents rated 1900 or higher.
These results are independent of style or geography (I've played in MN, Chicago, and NYC). So from my own personal experience, I think the curve is nonlinear.
Note: I'm not saying that a 1750 opponent is easier than a 1650 opponent for me. It is almost always the case that higher rated opponents are more difficult. What I'm saying is that a 1750 opponent is not proportionally more difficult than a 1650 opponent for me, on average. This means that there's some sort of nonlinearity that ELO isn't capturing...
Daniel Pi: Of course there is variation. Some people you do better against than others, perhaps even contrary to what ratings suggest. But on average the ratings work great. If I do really poorly against one guy who has a similar rating to me but do perfectly well against others at my rating, yeah, I'm going to think that one guy I do badly against is an anomaly.
Yeah, but it could be systematic variation. Like you could just do badly on average against all players in a certain rating interval, relative to how you perform against average players of a different interval. That's not just an anomoly at that point, it's systematic deviation. It just suggests that a mathematical model of chess strength should have multiple values.
But that might get ridiculously complicated. I am inclined to agree with you that ELO as it is tends to get it right vastly more often than not, and possibly more accurate complications are not worth the additional computation cost.
so your saying someone like emory tate would beat magnus