My two cents.
I really don’t think any Vanilla Civs have been hurt by the expansions, other than England and maybe Norway and America. And England is a funny case anyway.
Norway has had a rough ride. From the start, they were just in this nasty place where lots of mechanics they leveraged didn’t work well - Military Tactics, Pikemen, Coastal Cities, other people having Coastal Cities, and so on - but they maybe also suffered from having a gameplay style people didn’t get on board with. I think people for a while saw them as a conquest Civ, when really they’re an explore and raid Civ.
With the various balance changes in GS, I’m not sure Norway are really “underpowered” - they were sort of always underpowered given the explore / raid design but we’re fun regardless - but they do now feel a bit un-sexy compared to all the new kids. The basic design is fine - faith, early exploration, raiding, two unique units - and naval, coasts and faith have all got better in GS which helps them. But, yeah, they just need something to make them feel a little more exciting. Also, nerfing the Maori a bit would also help Norway feel more special.
America didn’t get hurt by any changes in RnF or GS. Instead, I think America just sucked regardless since Vanilla, because FXS gave them this very passive and insipid design (sorry FXS). All that’s really happened in RNF and GS is that these expansions provided an easy way to revisit this Civ’s UA. Really, they could have had the whole diplomatic cards into wild cards from the start. Regardless. America is in a good place now.
England was very unlucky. The game was originally balanced around
overlapping Industrial Zones and
stacking Harbour and Commercial Hub trade routes. FXS killed both and lots of Civs, including England, suddenly became a bit lost. Indeed, I think the whole balance of the game has been thrown out from the very start given the decision to nerf both mechanics. FXS have been inching towards solutions for both missing mechanics, but probably aren’t there yet.
Letting England keep the trade route stacking in Vanilla, a bit like how Inquisitors have been nerfed in GS but Spain has been allowed to keep their original design, sort of mitigated this change for England. But England still suffered from the underlying change in balance - getting rid of stacking meant coastal cities were weaker and naval less important so there was no one for England to compete with on the waves.
RnF then reworked trade routes, which royally screwed England, but really just made the problems with coastal cities even worse. And then FXS decided Pax B didn’t work with the new mechanics and the general desire to make conquest harder (they may have been right about that too), and then it became apparent FXS would rather recycle a lot of England’s design features with other Civs (Zulu gets Pax B; Sweden gets British Museum, various others get stuff England basically had in Civ V).
So, England started a mess and ended up a bigger mess. Reworking England therefore made sense.
I agree with
@Sostratus that the new England feels right when you read it (an empire of Iron and Coal) but in practice the new abilities are very underwhelming. Part of the problem is that England is again tied into mechanics that aren’t quite working - colonialism (okay, that’s been a problem from the start) and now power and Military Engineers. But FXS has done a good job of buffing harbours and coastal cities, and has found a good way for England to interact with trade routes, so overall England doesn’t feel like a mess anymore. Just a bit bland in places.
The more I think about it too, I really think the “power” bit of England’s WotW should have focused more on Factories and maybe even have had a negative “more CO2” mechanic. Anyway. Hopefully FXS haven’t got tired of messing with England, and will maybe give them another look in the patches.
God. I talk about England a lot. Sorry.
Anyway. Digression aside. All the other Vanilla Civs still seem well designed to me. If any have a problem, it’s just that they’re tied into mechanics that need more work or were maybe the Civ was a bit underpowered initially anyway. Really, I don’t think there are any other Civs that have been really hurt by new mechanics or overshadowed by new Civs, although there are a few that had designs that shined more with the newer mechanics (France and spies; all the Civs that focus on faith; Civs with abilities connected to City States).