MutilationWave
IDDQD
The ages system does do this mechanically, although, like many things, the numbers could be tuned better. The simple fact that you cannot research ahead of the era is massive. Notice what parts of "rubberbanding" players complain about - it's whenever they feel something is being taken away from them. Not when they are prevented from doing something nor when the opponent is given something (since all civs start an age at the same tech level, everyone is "given" missing techs.) Yet they all enjoy the games where there's a competitive rival and it's a close-run thing. This is a problem of presentation and design and it's not easy to solve.
This is so well put, especially regarding taking things away rather than preventing the player from having things. It's a big emotional reaction that's at the core of the hate of ages just as much as the intellectual hate directed at "ahistorical" civ switching.
I think some people are commingling their feelings about the things they lose on age change with the civ switch itself, without realizing it.
For me, civ is a fantasy game so I don't care at all about civ switching, it's the mechanics of age change that annoy me.
I think the people on the "ahistorical" facet of the issue could be placated with more civs to give a natural feeling progression. And who doesn't want more civs right?
Tuning the mechanics will be more difficult as you said. I think a big first step would be to just leave our damn units where they are, and don't change them into different types. I really like the commander-unit limits otherwise.
I would love to play a difficult game of civ 7, but it hasn't happened. I tried my first game on immortal because the game was new, no challenge then, no challenge on deity. I'm in favor of MORE rubberbanding. Good AI would be the best fix but that's a different discussion.