If I recall correctly, ICS was originally a thing because two size one cities were automatically better than a single size two. Besides the fact that you'd have two cities for building things, you'd be working four tiles (one outside tile plus the city center) instead of three. Never thought it was very fun, but many times it seemed you'd be best off just spamming settlers (which were also workers) to make one improvement and plant, only needing to leave one space for the new city to work. I think that another thing going its way is that you could buy whatever you wanted with money, and roads gave a gold. Going to extremes you'd wind up with a big checkerboard with small towns every other tile. Not a strategy expert here, but I think this is how it went: heck I didn't even need online strategy articles and the like to figure this out.
Many of the things they did to counter this aren't even brought up any more--minimum city distance from each other, upkeep, no rush buying early, etc. I actually liked what V did to make fewer, larger cities viable, but of course they probably went too far. I think they were always had the worry of returning to that in the back of their minds.