Sure. All I was saying is that it's theoretically possible for a market order that a customer submits online to be front-run (as opposed to a market order submitted to a single exchange). No clue how often it happens in practice.
It's theoretically possible and has always been for somebody to see order execution in progress and trade ahead of it. In practice, that's frequently just a side effect of somebody being so slow that their actions trigger quant algorithms, it's not a super profitable game trying to latency arb proper market sweeps anymore (not to say latency is not important in but, but it's usually for other reasons)