I like the idea of one unit, and I like the idea of a hex map instead of a grid map, but as you've all said the AI just can't handle it.
If you play soley multiplayer against other actual humans it's probably a perfectly good design. I wonder who plays civ that way though? I never did and I don't think very many people do. They're trying to make their game something it never was.
I guess you have to if you're unable to tackle the AI issues. it's not like I find a fault with them, I just don't enjoy their product anymore.
The modding community is what made CIV4 the masterpiece that it was.
I tried hard to play CIV5 but it just never clicked. I even enjoyed some of their systems more than CIV4. It's that AI problem, it's just too significant. Never even bought CIV6 or their sci-fi reskin of 5.
Performance started to get really really bad, too. It felt like the 90's with the load times for maps. I've read that it's a problem with coding your entire game in python. I dunno, it's what I've read, but I for sure know the performance of the engine went backwards.