Still much more players than INT, but also much much less than the JP of last year. And as with any online game, the amount of bad, mediocre and average skilled players far outweighs the amount of actually strong ones. So with the playerbase as a whole dwindling, the already rare powerhouse becomes even rarer, making it much more difficult to assemble an army of gods.
Before, damn near every group you ran into was an army of gods. People from INT would just sit in the merc registry and never get hired simply because there were better, more appealing options available. Japanese players hired mercs they recognized and knew could get results. It made the game feel very dead when it actually wasn't.
Yeah, getting hired as a merc on JP, when not using a meta setup is pretty rare, actually. Usually comes down to waiting until a nub starts spamming quick-hire, or you get a friend/return customer to come pick you up.
As for powerhouse merc teams, make no mistake, they're still out there. Usually the same handful of people that only play with one another. If you look closely at any teams you come across ranked S or higher, that have 3 mercs, you'll see a lot of the same names over and over again. Though, these aren't generally amazing players, overall. Just ones that abuse the meta, and swap between three or four reskins of the same builds.
Also, oddly enough, there is a trend for such players who seem to care about their W/L ratio, or team rank staying at SSS, for some reason, and will only play during the dead of night, Japan time, when the server isn't quite as active. This usually allows them to either play nubby teams, with or without UNACs, for easy wins, or to continually face the same team over and over again, using hard-counter strategies. Against the latter, they usually play until the other team hard-counters their hard-counter, take the loss, and then call it quits for the night.
Overall, though, yes, the numbers, even on JP server, have been thinning greatly. Most of the people that are left are in one of the two groups I mentioned above, with a couple nubbins scattered in here and there. Used to be that you could find a fight at any given time of day, just the variety of fights might not have been that diverse until certain hours. Now, you're going to be waiting a few between fights, even during peak hours, unless you're in the middle of fighting against the same team over and over again.
But, facts are facts. The game is old, and doesn't even have support from its devs anymore (Not that it did, once Dark Souls 2 was announced as a thing...). Aside from that, most people jumped ship to the PS4, to play Destiny, then Metal Gear/Dragon's Dogma, and now back to Destiny again... (Because, really, there aren't any other games worth owning on a PS4, right now...)