Launches are never 100% perfect, but people like OP like to overexaggerate how bad they are as well. WoD has been the only semi-recent expansion that has been notably bad.
MoP was fine - queues weren’t overboard, DC’s basically didn’t happen, and the only reason it was even a little messy was because of the intro quest to Pandaria being very script heavy and having 2000 people there at once. As soon as you got through it, you were in the clear.
Legion was totally smooth.
BfA was totally smooth.
We might get a little more lag than the last couple in Shadowlands since we all start in the same zone, but I fully expect it to be mostly smooth as well.
Yes, you should be prepared for your playtime to be diminished in case something happens, that’s logical, but launches are not typically trainwrecks.
I pray that one day we see another legion launch. Nobody remembers it because of how smooth it went. No lag, no bottlenecks, sharding was just introduced for the first time and was working well.
There will absolutely be bottlenecks this time around because the questing is linear the first time.
Extra long maintenance to fix things that suddenly go wrong.
Once that is done, and we can log on. Someone will start a DDoS.
Once that is over, and we actually get to start playing.
Servers will start having issues due to everyone being in the same
place trying to do the same things.
Im not even going to try to start until either Wed night, or Thurs morning.
You know where you are, right?