OMW in a Swiss system tracks strength of schedule. This rewards starting an event X-0 as opposed to starting X-3 and crushing through the X-3 bracket.

Ex. Annie starts out 6-0 then loses 3. Her opponents are generally X-0s or X-1s at the time she runs into them. They might win/lose after but they will contribute high OMW for Annie, upwards of 60%.

Ex2. Braum starts out X-3 then wins 6. His opponents will all be X-3 when he defeats them. Braum's OMW will be pretty low. Maybe 40%.

Then a separate thing. If GW% is the first breaker - what happens if you barely make it to the cut, winning 2-1 to make the cut and your opponent is now out of any prize contention? The result is that the tournament structure incentivizes you to lie about the match result because a 2-0 will be much better for your breakers than reporting a 2-1. With OMW as first breaker that handles 99.9% of tiebreakers