I thought techs behind a certain era are discounted, or is it just involving you?
In any case, it should be the case that you should receive a discount on techs known by more than a certain amount of civs.
Also I think cities themselves should cost maintenance. Cities with a governor or government building do not cost maintenance. This should scale with era and cities on different continents should cost more.
Yeah, the maintenance system in civ 4 was a good moderate limiter so that civs that expand too far ahead of their capacity struggle, or you could think of the corruption system in civ 3 as a similar limiter. Currently, the only thing that kind of does that are amenities, where a rapid expansion can drop you down. But it's only a minor factor, and still too easy to just snowball out of control, especially when you get later in the game, you start to gain more ways to add amenities in with only a minor cost that it doesn't really prevent you enough. Something like this might even play more to my style too if done correctly - in that, early in the game governor management is critical for survival, but later on, I just can't be bothered to move governors around other than managing loyalty if I am conquering people.
But yeah, overall, nobody wants a rubber-band mechanism to the level you get in Mario Kart where the person in first routinely gets knocked back to last, but one of the annoying aspects is that if I fall even a little behind early, I will often just give up because I know I really have no chance to make my way back in once you fall back.