There are several issues with the launch. I agree the DDos attacks are surprise to deal with.
I think it would have been better if devs prepared with alternative plans like Plan A, Plan B etc.
1) Engaging some third party security experts for dealing DDOS attacks, for example using cloudfare
2) Setting up Load balancers, if one VM is down, all the requests redirected to second one and so one. Setting up atleast 10 vms 2 days ago with private ip addresses and on launch day redirecting login.lisk.io to those.
3) On demand scaling, as the number of users increased , automatically setup to use more resources (Azure allow this).
gdax.com is also launching today and still offline using cloudflare, so basically it don't mean crap for the disruptions within first day time frame, don't matter how well you prepared, they're just pointing the ddos to it