The early access has primarily used lumberyard.
Well that's open to question. Yes, Roberts claimed they switched to Lumberyard in "two days" or something ridiculous, except in their infinite ineptitude they went on to release various Bugsmashers video episodes which clearly showed them working with CryEngine source code, and I seem to recall they were even advertising for a developer with experience using GUI tools which are native to CryEngine and not supplied with Lumberyard.
I wouldn't be surprised if they've been scrambling to erase all traces of CryEngine from their codebase ever since the lawsuit hit. It would certainly explain the minimal progress they've made with their actual games.
Take Derek's ego and all the other bullshit out of it.
Urgh, if only. He started off as an interesting and valuable counterpoint to Roberts' constant bullshit, but for the last year or two he's been almost equally unbearable.