There is effectively a CW-Hunt restriction in place during prime time, on EU that's anywhere from 16:00 to 23:00. WT is not available during this time as all servers have a full queue. Therefore, a restriction would do absolutely nothing to help the hunting situation. The problem isn't even that the zones can't handle 500+ players. They can safely do that, yet more often then not, hunts are killed when there are only 150-200 in a zone. The issue lies within the fact that only a extremely limited number of players can be transferred to a given zone per minute. If you watch the player number when trying to move between zones, you can see how low that number is (~50 players per minute). A simple short term solution would be to give each hunt a spawn protection, to at least allow the maximum number of players a zone can handle to kill it - you could compare it to the SS-Rank spawn condition.

Generally, S-Ranks are simple are an outdated system that didn't change since ARR, while the whole ecosystem around it changed. Significantly more players on each world, crossworld hunts/linkshells, achievements that require 1000 kills (if you get 10% of all CW spawns on EU, you'd need more then three years for the ShB achievement), etc. Long term, a proper solution therefore would be do rethink how hunts work, e.g. spawn timers, rewards, loot restrictions, respawn mechanics - e.g. hunts respawn quickly once triggered, but can only be looted once in that window