This isnt true vanilla expirience.
Blizzard servers never had caps this high and anything over 5k people online per server is bad for number of reasons.
Even if you fix the lag or delay or whatever you call it you are not adressing the issue of overpopulation.
Having over 10k people online on one server is not something you should be proud of. Its a problem.
Having over 10k people on multiple servers IS something you should be proud of and you can call it a successful project