Air that's flowed over the wings is going down. Air that's closer to the centerline is going down more, air that's further from the centreline is going down less.
Just take a look at Flightpath's pictures - especially the one immediately under "The aircraft wake is compressed, and with the combination of the 2 counter-rotating vortices"
That little symbol 'w' is downwash and the picture shows that the air closer to the centreline is going down a lot less than that near the tip. So I'm afraid your argument is not supported by the facts.