Magnus Carlsen's Elo rating is about 2870, and according to this quora answer, he hasn't lost a game in 100 games at the time of writing. Assuming that his win rate hasn't changed since then, and assuming this implies conservatively a win rate of 99%, then based on this table, which says that a 99% win rate against a single other player corresponds to about 670 ELO surplus, this seems to suggest that Magnus Carlsen plays players who have on average an Elo rating of 2200. Is this correct? it seems like it is way too low, given that my understanding is that the super grandmasters mostly play each other and other high-scoring grandmasters, at least in long games.
A 99% win rate is winning 99% of games played. Carlsen does not win nearly that many games, since at top level most games are drawn.
Carlsen's overall record in life is +1262 =1289 -454, which means 1262 wins, 1289 draws, 454 losses. He has won 42.00% of all the games he's been recorded to have played, and has an all-time average score of 63.44% (wins are 1 point, draws are 0.5 points, losses are 0 points).
Another thing is the amount of rating gained or lost depends on how strong your opponent is. If Carlsen were to play a beginner a hundred times, he'd win effortlessly for a 100% win rate - but he'd also gain almost no rating.
assuming this implies conservatively a win rate of 99%
There are a number of wrong assumptions in your question. First, at elite levels where players don't often lose it is draw rates that are high. Second, according to the FIDE rating rules if the rating difference were 670 it would be adjusted down to 400:
A difference in rating of more than 400 points shall be counted for rating purposes as though it were a difference of 400 points.
In fact over the last two years according to the data on FIDE's rating website for Carlsen he has won 40.7%, drawn 54.3% and lost 5% of his games.
Here are his results from November 2019 to date.
A "*" next to the average rating shows that some or all of his opponents were rated more than 400 points lower than him and their ratings were adjusted up to give him more rating points.
|Date||Results||Rating Change||Avg. opponents' ratings||Event|
|October 2021||+4=5-1||-0.2||2741||Norway Chess 2021|
|October 2021||+2=1-0||+0.3||2557*||36th European Chess Club Cup 2021|
|September 2021||+8=6-0||+8.4||2672||World Cup 2021|
|March 2021||+3=9-1||-15.3||2714||Tata Steel Masters 2021|
|November 2020||+5=3-2||-0.8||2743||Altibox Norway Chess 2020|
|April 2020||+1=0-0||+0.8||2462*||Ostlandsserien 2. div A 2019-2020 R 9-11|
|February 2020||+3=10-0||-9.6||2731||Tata Steel Masters 2020|
|January 2020||+1=3-0||-0.2||2778||London Chess Classic Grand Chess Tour Finals 2019 Standard Games|
|December 2019||+2=0-0||+1.6||2470*||Ostlandsserien 2. div A 2019-2020 Round 1-2|
|November 2019||+4=7-0||-6.0||2692||2019 FIDE Chess.com Grand Swiss|