So the big difference between the Virginia rally vs. Hogg's rally and whatnot:
Virginia was local to the state, DC rallies are national.
The fact that ~23,000 people showed up at a local state rally. National rallies have bus trips organized, flights paid for, etc. etc. etc. Now take that into account and you can easily multiple by 10 to get a more reasonable number if it were a national rally.
Everyone keeps saying "20k isn't much for a big rally." Bullshit.