Grindr has the largest share of users by far. I suspect SCRUFF is #2, both because it is almost as old, but also because they clearly skew towards a different segment of the community. I assume that Jack'd and Hornet are more popular in certain geographical areas.
But I agree with pretty much everything you say, except for wanting to emphasis that getting people to enter their status is crucial in helping to normalize regular testing, safe sex practices, and allowing HIV+ individuals to be open members of the community.
It's kind of funny, and while this wasn't always the case until I educated myself on it, but I trust/feel safer with people who are positive more than those who aren't in some ways. Having sex with something who is positive but undetectable (even unprotected) is better than having sex with someone who doesn't know their status. Even putting HIV aside people who are positive are being tested much more regularly than the general public. Similarly to people on PrEP as they are required to get tested (only for HIV but I know a number of people who also take the opportunity to get tested for other things) every 3 months.
But I agree with pretty much everything you say, except for wanting to emphasis that getting people to enter their status is crucial in helping to normalize regular testing, safe sex practices, and allowing HIV+ individuals to be open members of the community.