One of my favourites too, and I think I can articulate why.
it’s because to win the seals victory often involves alot of pressure from the Ai, and just tough enough indepenedents, that periodically spawn.
Plus the risk/reward calculus of controlling a seal makes it always a tense and interesting decision.
You need to put one unit ion a seal to control it after you conquer it, but every so often the guardians of teh seal will attack, and try and recapture it. So, do you leave just one unit, meaning any old wandering indie unit, or another player, can easily capture it, or do you camp on it.
And those are units you need to wage war on other players.
PLUS, and this is one for me that is imho huge, possibly key to the whole thing, capturing a seal starts the timer, capturing more seals accelerates the timer, losing seals slows or stops the timer, and holding a seal doesn’t make your empire stronger, in fact might well make it weaker (on account of having to guard it.) Plus, there’s a strong element of racing to be the first, as the loot is usually pretty good.
The doomsday victory otoh is very much something you do when you are already quite strong, and it just makes you stronger, and you control the sites anyway.
It is also something the AI is very well suited to playing, as it will, on higher difficulties, usually have many more units than you do.
I think Planetfall could have benefitted from having something more like the seals victory, i.e. an independent location on the map for you to fight over.
IIRC, there is a grails victory, which is in a way like that, i.e. you research anomalies until you decipher the grail locations, then go fight on those locations and eventually unlock the grail.
Which doesn’t give you victory immediately iirc, but gives you some very hefty bonuses.
Fairness maybe isn’t the right word. What I mean is it is a bit unfun to suddenly have your AI opponents spawn massive armies out of nowhere, or beeline to your undefended cities when they have no vision.
I.E, when the cheating is…well…blatant, it isn’t much fun.
But if the entire game is built around this, then it can be much more fun.
I have often thought how the end game in PF could be made more interesting, and one thing I liked, from RTS games of all places, is the idea of depleting resources.
So, your gold mines might start out at 20 per turn, but in the mid to late game they start to run out.
This could force/encourage conflict and end things quicker than the current status quo in 4x games where you either have a stalemate, or the player victory is assured but not finalised for another 20 plus turns.