Stacking wasn't perfect but even with stacks of doom it allowed for a balanced variety of viable playstyles. You pretty much have to cheese a min/max urban sprawl (iirc - it's been years) on Civ5 to beat the higher difficulty levels because of the differences in action economy, which undermines replayability. Replayability is the heart of Civ.

Some changes in G&K seemed like they were designed to patch the economics to a degree.

I was poor and didn't want to have to pay for a patch, so I ended up getting tired out on vanilla and didn't get into G&K much by the time I could justify buying it. But from the discussions I've seen the issue was too fundamental to simply be patched over. It's still a good game but Civ4 reigns as king imo.