That could also be solved by making each affinity indirectly generate bonus-science. Make it so Purity gets 3% Science per Virtue and there you go, spamming Culture-Improvements may suddenly be a strong choice, if the game-length was extended - while at the same time making it less valuable to stay on low-tech improvements.
Give Harmony a few more "per Population"-tools and biowell-heavy strategies would profit them most (if trade routes were brought down to a reasonable amount of food/production).
Supremacy could get a native science boost from their gpt like that one wonder already does.
And I'm pretty sure it wouldn't be too hard to find more of these things for hybrid-affinities.
Yeah, that would be one option, and one of the easier implementation wise. Another option would be to have some powerful lategame (affinity specific?) virtues that only unlock later in the game and justify the higher cost. Or just straight up buff the t2 and t3 synergy bonuses.
How easy would it be to add another condition to building the wonder? For example, purity needs 20 virtues to build the wonder, harmony a city with 30 population, or supremacy a high energy surplus. This would certainly make the victories more distinct and force you into different play styles. I think this could be a simple yet refreshing change to the victories
And this is another option. I would prefer something more complex still, but this would be a start.
Ideally though, I would like to see some actual tension between the affinities going for the affinity VC with only maybe the contact victory remaining the "wait X turns" type. I don't have the whole picture in my head yet, but some basic things that can be added:
-Affinity victory conditions clash with each other. It might be more difficult to get refugees from Earth when someone else is sending troops to "liberate" them. E.g. sending troops through emancipation gate limits the spawn rate of earthing settlers. Likewise it might be difficult (or outright impossible) to achieve transcendence in a heavily terraformed or industrialized world. This would force harmony players to attack the onces who clear miasma and spam terrascapes or manufactoeirs.
-Higher emphasis on terraforming. Already mentioned a bit in the previous item. Harmony players should be encouraged to leave the planet in its natural state while building some eco friendly improvements. They should get bonuses from tiles with forest or miasma and be able to regrow forests etc. Supremacy players should be encouraged to just pump up production and energy ignoring any ecological problems. Purity players should be encouraged to terraform.
-Create some affinity tension akin to civ5 religion tension. Your population should too have different views on the future of humanity. It should be required to have your affinity as dominant in your cities to even have a shot at the VC.
Example of potential changes to illustrate the idea:
Miasma - miasma reduces food on the tile by -x. Also each tile of miasma reduces health of ALL nearby cities in y tile radius regardless of the owner by some small value. Harmony later can reverse the effects and gain food and health. Supremacy can later ignore the health penalty. Also increases harmony tension in nearby cities.
Alien nests - Increase harmony tension in nearby cities. Can later be worked by harmony players for extra yields. Supremacy and purity players can build unique improvements on nests that remove the tension (and stop aliens spawns) and also get additional yields (supremacy uses them for labour adding production and purity builds preserves that give culture). Simply pillaging the nest also removes tension.
Forests - biowells built in forests grant extra food. Increase harmony and purity tension by equal amount.
Mines, quarries and manufactories - reduce health of all cities in x tile radius by a small ammount regardless of the owner (pollution). Supremacy players later ignore the penalty.
Domes - negate health penalties from nearby miasma and production improvements (by x per dome, up to 0 penalty).
Terrascapes - greatly increase purity tension. If pollution and misma health penalties in a city with terrascapes reaches x all terrascape yields are reduced. Otherwise give a large health bonus.
Nodes - increase supremacy tension. Manufactories gain a production boost for adjacent nodes.
Arrays - Greatly increase supremacy tension.
New unique traits:
Supremacy
-Tolerance: population ignores pollution and miasma health penalties. Cyborgs just don't care.
-Global network: Gain health and science bonuses for each city connected to the capital. Later on connections can be established with satelites. Science penalties for city count for connected cities are also reduced.
-Collaboration: gain +x science for each supremacy follower in the world.
-Humanity 2.0 (endgame ability): Population no longer generates unhealth or consumes food. All excess health is added directly to science. Population no longer growth naturally. Can convert production to food at 100% rate to grow.
Harmony
-Adaptation: Gain health and food bonuses for miasma instead of penalties.
-Ecoscaping: Gain extra food from forest tiles. Can grow forests with workers.
-Swarm intelligence: Gain +x% science per pop in city (encourages tall cities).
-Biomanufactoring (endgame ability): x% of city food is added to production.
Purity
-Purity of thought: Garrisoned troops increase purity tension. Can chose to "purify" conquered cities by killing all non purity followers. Min 1 pop remains.
-Rigteous cause: Cities spawn free units, rate depends on the culture output.
-Ideological sciences - +x% science for each adopted virtue (as suggested by Ryika)
-Holy war (endgame ability): - +x% combat strength near cities where purity is the dominant affinity. x% of culture output is added to energy.
Tension:
Basically the same as civ 5 religion. Each affinity tension determines the % of followers of the given affinity in a city. Progressive penalties for the number of citizens of non dominant affinity (going hybrid allows to tolerate two affinities).
Victory conditions:
Can only be attempted if >50% of empire pop is of the appropriate affinity. Transcendence speed depends on # of forest and miasma tiles worldwide. Earthling settlers can not be settled if miasma/pollution is above certain level in the area. Additionally they can not be spawned on a turn when a unit entered emancipation gate on the previous turn. Can put units into the exodus gate instead to protect Earth (reduces the supremacy VC counter).