means you drain rating from the total pool
Ratings aren't zero-sum. In QM, due to the modifications to TrueSkill (halved rating decline below QM500), virtually everyone is a rating donor to the overall pool (yes, a high-rated player is going to have asymmetric outcomes because of matchmaking, but 1) that's how any skill-rating system works- the win/loss outcomes aren't symmetric, but both exchanges are and the expected outcome is 0- and 2) over a large number of games everyone's rating trends upwards).
In a normal Elo ladder, everyone just adds the average rating to the total pool. If you're worse than the average player (from before you joined), you inflate everyone else's ratings by donating the gap between your true/equilibrium rating and the average rating. If you're better than the average player (from before you joined), you deflate everyone else's ratings by withdrawing the gap between your true/equilibrium rating and the average rating. E.g., if a "true" 1926-rated player joins the 1v1 ladder today with 426 players, their impact at Elo equilibrium will be to deflate everyone else's ratings by 1 point; if a "true" 1074-rated player joins, 1501 becomes the new 1500 (in the long run).
In QM, you grow the pool (including your account) because of the safeguards around rating loss resulting in asymmetric rating exchanges (ignoring mu/sigma, which makes truly symmetric rating exchanges less common). Every <QM500 loss of yours grows the pool by half the stakes, by growing your opponent's rating more than it shrinks yours.
So this thousand-account cheater would wind up donating to the QM rating pool. If they're able to aggregate most of the QM rating themselves, that would require them to have a high stable rating themselves.
Beneath the modifications, QM
is a valid skill-rating system (if everyone keeps playing forever). The rating at which you reach a 90.9% (10/11) win rate (10 +1's, 1 -10) is your "true"/equilibrium rating. It's just that once you get close-ish to your rating (when you break QM matchmaking), it takes forever to reach your true rating since you'll hardly even notice if your real win rate is 95% and not 91%. So to execute the rating-aggregation attack you described, you'd have to deserve that high a rating in the first place anyway.
Functionally all you're describing is being very good at QM and having a bunch of accounts all converge to your true rating (while all inflate QM ratings in the process). You're eating up a large percentage share, sure, just like what would happen if Rufus played the MTL with 10 accounts, and you're generating the usual rating deflation that happens when a higher-than-average-skill player joins a ladder (10 Rufuses on the MTL would make 1440 the new 1500), but even that is significantly offset by the rating inflation from QM's safeguards. This isn't rating manipulation; it's just being good, at scale.
Edited 10/1/2021 23:44:11