This is something that comes up a lot, something I've studied and discussed with my game group, and something I felt deserved sharing for the sake of people seeing. You can take this as a complement or criticisim of the game. Either way it is what it is.
Ok. So the Ascendency Victory is basically a game "clock" to count the game down to an end result. It keeps things tense and active and encourages interaction with the knowledge no one can turtle in this game unless they get an excellent Culture Infrastructure happening.
So anyway, lets look at how this thing actually works:
First, lets get the obvious covered - the goal for an AV (ascendency Victory) is to accumulate 5 Ascendancy. You start with 1 Ascendency (unless you play the variant you start with 0) so you simply need to get +4 more Ascendency to win the game.
To increase Ascendancy you need to spend 5 Culture. Thus, to get from 1 Ascendency to 5 Ascendency, you need to save up 20 Culture to spend. AND given you start with 3 or 4 Culture (depending on you Varient for starting reasouces) that means you need only 16-17 Culture.
Given EVERY homeworld starts with 1 Culture Node, any player will win the game in 16/17 Turns provided:
1) They do not spend any Culture (aka build Culture Nodes, Colonise Worlds, or attempt Hegemony)
2) They do not lose their Homeworld's Culture node (aka are Invaded).
Pretty straight forward. The implication being, given you have to spend Culture, the number of turns before the game ends will typically be around 20 turns. Which is a decent amount of time.
HOWEVER, this is VERY misleading as this "clock" drops VERY fast.
Consider this scenario:
On turn 1, you explore and find a system. Given there are 27 discs to explore, 8 of which have Culture Nodes and 6 which have Open Nodes (which can have a Culture Node), there is approx a 50% chance any system you will find will support a Culture Node.
Thus, once a location is discovered and with your starting 3 Culture, you can have a 2nd Culture Node as early as your second turn (i.e.:
-1 Culture to Colonize the World, -2 to place a new Culture Node).
Now while this DOES eat your Culture stockpile by -3 (essentially increasing the game length by -3 turns) you have now DOUBLED your Culture production for all future turns.
So with your starting Ascendency of 1, needing to gain 20 Culture for the AV, and now earning +2 Culture/ turn, you will end the game in 10 turns starting from turn 2 (again, provide you aren't spending it on Hegemony, Colonization, etc...). That means the game will end in 11 turns (1st turn to setup the +2 Culture per turn to accumulate 20 Culture for a Win).
There is more beyond that too (future Culture Nodes being built, costs for other stuff, etc...) but that should give you all the very key breakdown to how the mechanics of this works.
Feel fre to use this to explain why you are correct about your view on the speed of the game :)
I see Ascendancy has a 3 credit system, a common (production) an uncommon (research) and a rare (culture) which you need to win the game. However the homeworld requirement is a cap against a "culture rush" strategy. Also with supremacy victory it does put research at a higher value as research does seem to have more combat/hegemony advantages than culture advantages (except for romulans).
So far these are some generalized strategies.
Federation Culture Rush
Romulan Tech/Culture Rush
Ferengi production rush (100 production = win).