My take is that ancient era techs should be split up so that there more ancient era techs overall, but a greater total research cost than at current. That way the early unlocks that actually provide the initial game content can be researched at a fair rate, but with less immediate impact, and the ancient era will still feel longer overall.Maybe revert the ancient era tech costs back but increase the costs of classical era techs or revert the costs of just 2-3 starting rows of techs?
This gives the opportunity to separate discovery of limestone from building Stonehedge/Pyramids, and maybe push the Greath Baths later too. This would have a double benefit as it's very difficult to build these wonders on higher difficulties, since the AI already starts with techs needed to reach those wonders, and has the research bonus and hammer bonus to close on them before the player, at a time when the player has no real means to challenge that advantage. It would be nice to feel like I could actually try for them.
Also an opportunity to add more religion/cult related techs.
I think the core of it is that the ancient era felt slow because there was so little to do in it. The first 100-200 turns fly by because you move a unit, click end turn, and repeat. There are very few decisions to do or interactions to have that flesh out the gameplay at this time, so it feels shorter than later eras. Increasing the research costs of techs just means you're doing that same unengaging loop for longer. There might be more real time passed before you see the classical era splash screen, but the gameplay isn't any more interesting or engaging. The fix doesn't even have to be a longer ancient era, it just needs to make the existing ancient era have more to do. That's easier said than done (and might even spoil the feeling of a fledgling civilization), so I still feel the best option is to make longer total research through a greater number of cheaper techs.