Hey! Fellow gay new-ish to DC here (moved fall 2021)

1. New York is gonna be more finance-centric
2. DC is just barely cheaper but they will both be wildly expensive compared to Utah. As an aside, I hope your salary estimate is based on Utah and you are just failing to account for a cost-of-living raise in a lateral move to NY/DC. 70-80K for a finance job in these cities is low. Like, first-job-out-of-college low.
3. There are a TON of dating opportunities in DC for 20s-30s gay men. We actually have the highest per-capita concentration of gay men in America. NY will have more gay people and gay bars in total but DC's gay scene is fantastic. In my opinion we're a bit more welcoming/chill than NY.
4. Similar to all of the above, NY will have a greater total simply because it's so much bigger. But DC has more than enough- it's impossible to do everything in either city.
5. I had a lot of success joining gay social/sport leagues. DC is still almost entirely remote work so things like office friends don't really exist anymore. In either city I'd suggest picking a few hobbies/activities/sports and joining groups associated with that thing.