Increase the value of large cities would not help playing small (what people here calls tall) relative stronger as a large empire can still have as large cities and more of them.
The problem is that large cities are currently penalised. There is at least one veteran player on this board who intentionally limits their cities to 10 pop because beyond that the costs for them at least) outweigh the benefits.
Sure, a wide empire can eventually get all their cities to be large and so eventually have it both wide and tall. But really that should be an investment. At the moment there is just little reason to specifically go tall. Wide but not tall empires can crank out units pretty quickly, need less amenities per pop, plus are an investment in the future, as you said. There need to be more advantages to going tall.
The logical step is to make tall cities the quick, rush type the strategy, then have wide be the long term pay off strategy where it takes a while to get there (you have to have small cities as you use resources to create more cities rather than growing the ones you already have) but eventually you get many large cities.
In the short term, going tall would be best because you get those perks and maybe overwhelm those who are going wide. In the long run, wide isnbetter because eventually you'll have double or treble the number of cities each of a rough parity to the cities of the tall empire, giving a strong advantage there.
I don't know all the answers, but it makes little sense to me that I should be seeking to limiting my city sizes in order to get the best stats, nor that there isna "right way" and a "wrong way" to do it.