EC is only going to be as good as the community of modders who support it. Basically, most 2D people wanted EC features in their 2D client. Therefore, time to time, 2D art, or replica art, has been added to the EC client in order to make that client more like 2D. Why didn't EA just rebuild the 2D client from scratch?
QFT.
They did try to build the 2D client from scratch - It was called Kingdom Reborn.
To the OP:
As has been stated, the BIGGEST issue with EC (and by proxy, KR) was the graphics.
In the instance of KR, the style was almost completely different. Resolution was there, but for many of us, it didn't LOOK like it was in the style of UO. See Saphireena's high-res challenge for what a high-res UO should look like.
In the instance of EC, they tried to tried to bring CC's style back into it, which was good. But they didn't clean it up to fit the new engine, and what's worse, they tried to hybridize it with KR. So now in EC, I look like a fuzzy man with a trashcan on his head, which is the absolute worse of both client mindsets.
And in both cases, scale has been an issue. And for some, apparently, motion sickness.
Hands down, the EC UI is fantastic, and the client is much more stable than KR was. Modders have already done some wonderful things, like DermottLS' Enhanced Copper. I think on the whole, it's even better than CC with UOAssist once you get used to it.
So when I don't care what I look like, or when I need to take advantage of the incredible UI, I use EC. When I'm RP'ing, or want to see what something SHOULD look like (Like my house), I use CC + UOA. And I understand UOA is good for vendors as well, though I couldn't say because I don't have one.. Yet. And it'd be nice if someone could get EC to do bag sorting like UOA too.. That's probably the feature of UOA I'd miss the most.
And for all you're rabble-rousing, you're forgetting the BIGGEST holdup to adaptation and progression - the Devs.
If they would just stop making excuses, do the hard leg work of redoing the artwork in the same palette and style of CC and make it crisp, you'd have a much, much higher adoption rate, and would get more people to try it than currently do.
Yes, I'm aware some would never switch no matter what for any reason. I'm not talking about those people. More people would give it a fair shake if and potentially adapt if they cleaned it up. Enough to probably make the argument that CC users are in the minority and they could discontinue it.
.. Which I agree would be great for UO, if they could get the artwork together...
AND FIX MY DAMN TRASH CAN HEAD! (Sorry, I add this line to every EC discussion.. Not quite used enough to put in my Sig yet).