I don't think there's anything else to add than what they've said. All of this, aside from possibly the way the MSQ was designed, comes down to server congestion. They didn't prepare for it adequately, and it isn't a problem you can solve as an afterthought over a day or two.

It's a problem that's here to stay for quite some time until they add new servers and facilitate transfering to those. I reckon their "plan" was to just muddle through the first week and hope the amount of simultaneous players simply balances out.
Except at this rate, it'll balance out because players simply stop trying to log in and cancel their subs. This is 2017, not 2007, and far from the standard of any MMO launch.