I disagree with this. In the dichotomy between realism and "cartoony", Civ 1 and Civ 2 both kept a middle ground, where some of the depictions go for realism and some are more stylized. How much this was a deliberate decision or not is hard to guess.
In the case of Civ 1 the resolution was so low, that the finished product doesn't look overtly realistic or "cartoony" in the end. This is par of the course for many games in 320x200, which often are open to interpretation. But have a look at the mountains and forests in this example. They are clearly going for a "photorealistic" satellite look here, like in Civ 3 and Civ 5.
Orders list
www.mobygames.com
In Civ 2 the main map did get a little more abstract and unreal look than in Civ 1, with clear representations of cities and units standing out from the terrain by being depicted in a different angle. The way the units and cities are drawn could be described as "cartoony" or just stylized, but if cartoony, it is a very moderate cartoon style that respects proportions. On the other hand the game used a lot of FMV with real footage or 3D graphics, increasing the realism.
Standard view - two tanks attacking San Francisco
www.mobygames.com
Civ 3 went for a very realistic style, with the exception of the leader graphics, which were caricatured, though not in the excessive way that they were in Civ 6. The terrain and the units have a very realistic look to them, as far as what the confines of the technology and overall abstract representation allowed.
These War Chariots are the special unit of the Egyptians. A victory triggers the golden age for this civilization.
www.mobygames.com
Civ 4 mostly went in a more "cartoony" direction than Civ 3, but in a far less excessive way than Civ Revolutions or Civ 6.
By holding the right-mouse button over enemy units, you can view a readout on your odds of winning a battle against them.
www.mobygames.com
Civ 5 went for a more realistic look which was very stunning when it was new, and which I think still looks very good.
This Frigate has earned enough XP for a promotion.
www.mobygames.com
And then there's Civ 6 of course.
Screenshot from Steam
www.mobygames.com