For the few years I compiled pages about attendees at WMOC and their results (no longer on OUSA website) there were about 35-45 attendees, most of whom would also attend NAOC. So potentially a relatively large impact, but in a pandemic year, who knows?
I feel like the impact is much larger when you consider the international participants. Big overlap between the kind of people who would want to travel to NAOC and to WMOC.
Gah, maybe IOF doesn't actually want to grow the sport outside of Europe?
They are purposesly pitting WMOC against NAOC to shore up the (checks notes) Hungarian Orienteering market rather than build a big event and legacy in the Bay Area of the California (aka, 5th largest global economy).
If I was those Masters Orienteering Euro Tours filled with retired Swedes, I'd be annoyed. Wine tasting versus goulash.
It's quite possible all those retired Swedes will be wary of traveling to the US this summer, even if allowed to, and the fact that the events overlap will make the decision easier.