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The kinds of USB webcams that would be appropriate are those that do compression internally, typically to MJPEG. Then the Omega2 just needs to move data, not do any video compression or transcoding.
As a succession of individually compressed still images, MJPEG is less efficient than a true motion video codec, so the required bandwidth is higher.
To change that you either need a camera that encodes to a more efficient format, or an embedded computer capable of transcoding to one.
Basically the MT7688 is meant to be a router, not a "thinker" - granted as a modern device it's powerful enough to do fairly complex "think" tasks at moderate speed, but it wasn't built to be a fast processor for data and especially not for video.
Note that throughput and range are different subjects, but often in practice tradeoffs, as achievable throughput tends to degrade with distance, both because the bandwidth of weaker links is lower, and because of the increasing occurrence of errors requiring re-transmission (or at least dropping of bad data).