I'm not opposed to the idea of lots of small cities being more effective than few large cities. Civ 6 was originally built to favour wide and move away from Civ 5's 4 city meta. I think that's a good call on the whole, as it leads to more conflict over land and more dynamic situations. I think the ideal balance would be that a civ with few, tall cities produces more science per city than that of a wide civ with many low pop cities. However, overall the wide civ should have more total yields due to them controlling more land. I can see Rationalism finding a place amongst those tall empires with few cities, making those cities a little more efficient. Where as wide empires can't really pursue it without running into amenity issues, but still have the overall advantage due to shear number of cities. That theory starts to lose steam though when you consider the amenity system. Amenities should be there to act as a soft cap on total empire population, causing the player to choose either a wide play style with low pop, or a tall playstyle with few cities, or somewhere in between. However, going wide means you can also grab more luxuries, found more national parks and so on. Wide cities will also rarely drop below displeased due to the way amenities work too. One option would be to buff the Audience Chamber, so that it gives extra amenities to cities with governors, or maybe extra yields based on population to cities with governors. It's effectively the point in the game where your choice of building should reflect whether your going wide, tall, or focusing on conquest. If you could get a bigger rewarded for growing a small, tall empire, then getting the bonus from rationalism would just be the cherry on top. Tall doesn't need to be better than wide, but it should be able to compete.