There's a couple countermeasures they've used to deal with congestion in the past. They turned on the afk boot before and they also turned on mirrored open world zones, where there were instances for each zone and it would place you in one randomly if you teleported to that zone. For example, two players would teleport to the same zone, but you would be in 1 and they would be in 2, so you would never see each other. This made hunts a hassle to get to unless you entered the zone by the actual border. They actually kept that feature up longer on the high pop worlds when congestion was really bad back then, which means they monitor it closely. So if they're not using these anymore then it's clearly not needed, it might be when stormblood is live though.