And Blizzard as a whole have learned a LOT from that. If they haven't, they wouldn't still be making best-selling games after 20 years.
Besides, other than a few overpopulated realms suffering during Mists' launch, that was the smoothest Blizzard launch I have ever seen. They learn and improve all the time.
There is a major difference between the two. One is connecting to essentially 'one' server (not really how reality works, but there's more load on one than there are over many), and I don't mean authentication. The other is connecting to a variety of servers.