Because scores aren't weighted after victory, score basically just becomes who had the largest empire. If you pull off a science victory with just 4 cities on turn 210, you've really done something amazing and you get -- 900 points?
If scores were weighted after victory like in Civ4, that could make sense. A lot would still depend on how we arrived at the base score, of course. As an example, I believe you still just get 10 points for founding a religion or 0 if you don't. Ok, that's fine, but if I spread my religion to everyone in the game and win a RV -- I still get just a measly ten points? At least techs, civics, wonders, and "empire" (# of cities + # of tiles) slowly increase as the game goes on.
I dunno if religion points still work that way (I almost always disable score victory because it's fairly pointless when playing on anything king and above), but it's just an example of how going for certain victories will get you a lot more base points than other victories. As it stands right now, domination will get you the most base points because it directly contributes to empire score points as well as wonder score points via capturing cities with a wonder.
Anyways, I do agree with the OP, at least the heart of the argument.
I don't really judge my own victories by what turn it was when I won. I judge my own victories in an ad hoc manner. Was it an interesting victory? Was it fun? Was it efficient? Where there points in the game where I was on the road to defeat and then came out on top? Was I doing well in other victory conditions as well? Did I successfully use diplomacy to help my victory (usually by keeping rivals off my back)?
Efficiency isn't everything although victory on what turn is really the only objective tool we have to judge how good a strategy is. But having fun isn't objective. As an example, Korea is a very good science civ but I find them to be one of the more uninteresting civs for a variety of reasons. The only real strat you have to remember is not to put other districts near seowons (or do that only if necessary) and put farms mines next to seowons. Other than that, it's just spamming seowons, turtling up with hwachas, putting governors in your highest science and culture cities, and knowing what great scientists to gun for and which to pass on.