I like this definition of tall vs wide. I don't have a problem with large empires being overall more powerful than smaller empires, because that's how it works in real life too. What I would like to see is more benefit for those empires that space their cities far apart from each other so that they can work tons of tiles and run lots of specialists. Currently, when given the exact same amount of territory to work with, it's better to cram more cities 3-4 spaces apart in this territory than it is to build the cities 6 spaces apart, because more cities means more trading routes, more campuses loaded with all the science buildings etc. It's also easier to cover multiple cities with factories and entertainment districts when spaced close together, not to mention the closer distance means it's easier for cities to protect each other. Buffing tall play would also help relieve some of the tedium of having to micro so many cities and re-assigning trade routes constantly.