Hey. In fact, I created MyAion. These numbers are directly from aion classic kinah login packets that were sent to users. NCWest was testing stability of their server at launch and had a server capacity of 500 online users. The capacity was gradually increased until they reached current settings. We had queues right after the launch. However, the queue numbers were not the correct ones. It is likely that it was caused by changing login server settings.
Class breakdown on server's page shows characters only added to MyAion which is not an online character and not all characters registered. The MyAion DPS Meter version is for classic servers and doesn't have many characters available for upload.
The capacity of NA's Siel or Israphel is 9000. Also, you can check the exact amount of characters on the internet (for NA, RU and JP regions) by hovering your mouse over the percentage bar. Other regions do not have exact online numbers or capacity of servers. They share only percentages. However, you are able to use the search feature to determine the server's capacity while playing. It is possible to get up to 10 characters from the search result. If there are multiple players playing online, you'll be required to divide your results according to level or class. When I last made it for EU Stormwing Stormwing server It was set to only 3000 players. Prior to when KR changed their approach to sharing just percentage values, they had assigned capacity 12000 to Israphel, Nazekan and 10000 for Zikel, Vaziel. While they kept the exact number and capacity secret, three more KR classic servers were also added.
Don't forget that EU has less server capacity. The last time I've assessed Stormwing's maximum capacity, it was just 3000. But , yeah Aion in EU always had a higher population, so Classic is expected to bring even more people in EU.
I would guess it will take around 3-6 months to get the hype to go down and most of the avid gamers to be done with the present grind of gear and content. The chart of the top players, that I've added to the other comment, shows that the figures are slowly declining.
In addition, how is the balance of factions? I'm thinking about doing an elyos siel since back in the past, it was used as an asmo. However, wondering which are the main disadvantages in euro aion classic buy kinah doing so. Playing with Aussie wifi so not too focused on pvp. I just want to play around and pve/overworld with my chanter mostly.