> Which means they're rapidly coming to a position which will easily allow them to game the system (what used to be known as "cornering the market").
These are flows, not ownership.
Also, taking Citadel as an example, a vast portion of these flows are not their own, but rather thirs parties offloading their flows to them, so they have the underlying best execution guarantee to provide.
An other way to look at it is that investors are moving away from traditional brokers to execute their flows, because these HFT firms have become so good. So instead, investors offload their flows to HFTs acting as DMM instead.
Which means they're rapidly coming to a position which will easily allow them to game the system (what used to be known as "cornering the market").
I even wonder if their system has already learned cornering by itself via stochastic gradient descent.