You pretty much hit upon my exact feelings on the codex. There were so many ways that this book could have been inclusive to the old craftworlds while maintaining balance. Whats sad is that they even had a template to follow, in the form of doctrines from the SM and IG codexes. But all this book does is pidgeon hole the list if you want to be competitive, just like the Thorpian abomination that was the 3rd ed vanilla codex did.
Brushing aside game balance concerns, for the moment, there were a couple simple things that they could have done to make armies much more diverse and better retain the craftworlds.
1) Auratauch gets an Aspect Retinue. That Aspect now counts as a troops choice. This would solve the issue that the Auratauch is somehow the only man-sized HQ choince since 4th to not have a dedicated retinue, and still let Beil Tan players have their lists. While you are at it, Clowns need to be a 0-1 because they so massively outclass all other elite choices at present, to the point of making them obsolete.
2) 5 Wraithguard as troops. Spirit Seers mandatory. Honestly, no one is going to field a 400 point squad with 12" range that can be destroyed by one power fist squad. Further, Fire Dragons outclass them in every way that matters at half the price in the same slot, currently.
3) War Walkers as Fast Attack. Sentinals are FA, Dreads are Elites, Tornadoes are FA, but the fragile scouty Walker has to compete with the likes of Prisms and Falcons.
Honorable mention goes to Dark Reapers, who really have no good place to be in the codex. They are not tank hunters, stack up abysmally against all other HS choices, elites are wall to wall as it is, and their weapons are too good to be core troops. They are the Shining Spears of this codex, and its not like they were very good before either. Aside from giving them all EMLs (SM Devs with MLs are still cheaper than curent Dires anyhow, with better stat line) I have no idea how you would go about fixing them.
There are other issues with the codex beyond the sudden non-exitance of the craft worlds, like how ridiculously good clowns are compared to aspect warriors, but this one is central screwing a lot of veteran Eldar players out of being able to table their existing armies, which makes it the first 4th edition era codex to do this. Yes the Ultwe Infinate council and disruption rolls were abominations in their day, though the disruption table ceased to matter in the era of the pod. Simple fixes like the above would have accomadated a lot of people without altering game balance to a large degree.