Grand Strategy and 4X games are different genres for a reason: they're not meant to scratch the same itch.
E:FE is along the lines of Civilization, just with magic and tactical battles thrown in, and some seriously beefed up barbarians and goodie huts. I've not yet had time to really get into it, but maybe 4 hours in it looks full of all kinds of promise.
We've all been in betas before, and we know that "not-quite finished" doesn't mean "crash crash crash." And this is the same engine that was released more than a year ago.
Your past experiences with public game betas are not necessarily relevant to future public game betas, and indeed aren't in this case. Stardock has been abundantly clear that the object of the beta at this stage, is to squish bugs and to decide whether E:FE is feature complete.
As for why it's so damn buggy, there's three reasons:
Firstly, E:FE has been re-written to be much more massively multithreaded. This is a good thing because it has made the game both less CPU intensive and faster. But it's also extremely hard create, and that most of it is re-jiggering of a kind does not make it any less hard to fuck up.
Secondly, most of the graphics have been fiddled with in some way since W:WoM, and a fair chunk of new assets added. Unfortunately, from an ease-of-fuckup perspective, there's very little difference between new and modified. New assets have a couple of additional steps you can fuck up, while modified has the existing code-salad to fuck up.
Thirdly, while you might want to think Stardock is some massive transnational in the same league as EA, the fact is they're in the low end of middle-ware and do their own funding. That means they're not capable of bug testing privately to the extent you know from AA and AAA titles. They're ambitious enough to release massively complex games built on entirely new technology anyway, because they're cool little nerds. But they're cool little nerds who needs to do public bug testing to get their shit working reasonably well.