A good proportion I bet, but they didn't meet on a dating app.
Dating apps are used by people trying to "catch other fish in the sea". They want to expand their selection to social groups outside their immediate one, and date in a way that doesn't impact their status within their current group. If all your friends know Jack, and you dump him, word will get around for better or worse.
Your Jack example is true if you and Jack share a considerable amount of mutual friends. But almost all the people I meet on Tinder only have a couple mutual friends with me, no more. Often just one. Any sort of failures in our relationship don't have that much reach, yet I still have benefits like being able to query my mutual friend about that person, or leverage them in some other way like having them invite us both to an event to get the ball rolling.
I live in Tasmania, the whole island has a population of about 512,000. If you exclude friends of friends of friends, that's pretty much everyone here.
Still, Australia's top 5 cities have about 64% of the population. If you live in any of the non-top-five and exclude friends of friends of friends, that's a fair chunk of the locals.