And were you certain you would have won before an AI won a science victory? I do believe you, by the way, but I wanted to check how certain you were.
I suppose not - though, judging by the units I was facing -- it sure seemed like I had to have had a fairly decent tech lead... maybe they didn't upgrade or never built newer units, I don't know (all the AIs except the last one I conquered were constantly in debt). I just Sunday discovered the Victory conditions icon - and already deleted that deity game (the lack of time stamp/inverse chron order in save games means I pretty much zero out saves every time I quit a game) - so I guess it's possible the AI was on the cusp of winning via culture, science, or space race (I had seen a smattering of spaceship thrusters built... no other modules that I recall though).
That said, though -- "winning", for me at least, was always besides the point. I still cannot beat IV/BTS/RoM-AND (especially) when I start a game at a emperor or above (at least, not without either a dynamite start or a fair bit of cheating). The journey was always more fun than whether I won or lost.
I've tried of late to take less advantage of the AI -- House Rules around conquests, playing peacefully (I actually prefer to play as a dove/builder anyway) -- but the problem is, if you're going to war, there's just not a lot TO do.
Social Policies were neat - I still like the concept - but now they feel 'rote'... I find the decisions to be more or less automatic/push-button.... Big empire? Liberty + Piety + Commercial + Order. Science/space race? Tradition + Rationalism + Patronage. Culture? Piety for the 2 free policies.
It's the same with buildings -- the "do not cross" swim-lanes really take a lot of out of the game. On one hand, I'm spoiled by RoM/AND -- where buildings crossed multiple boundaries and were highly resource-centric. But - even in vanilla - buildings had multiple uses.... Religious buildings were more than just happiness -- they spread religion, they had commerce bonuses associated with certain wonders, you even science boosts (monasteries). Even simple granaries -- improved health + 50% pop per growht.
I have no problem with games that are easy to win.
My favorite sports sim is the OOTP series - but it's incredibly easy to snooker the AI in trades, and you can go from worst to first by just keeping an eye on the waiver wire. However - the journey is so much fun that I don't care. I've spent hundreds of hours building my dynasties.
I likewise love the Hoi2 series from Paradox -- yes -- I can turn the world grey as Germany - or most other majors - easily... but I still like the journey. As many times as I've Barbarossa'ed the USSR into submission, and done it in just 6-8 weeks -- I still enjoy the process of constructing my army, positioning everyone properly, then watching as my masterpiece of planning carves up huge encircled pockets.
Of course, being 'difficult' to beat adds a lot of replayability... but so long as the journey is fun, so long as I'm enjoying other aspects of gameplay -- I can live with that.
So - my real problem isn't so much that I can squash the AI whenever I so choose.... my problem is that the alternatives to doing that just aren't very interesting. Pick a win type and just do a whole lot of "Next Turn.... Next Turn..."
It really pains me - as someone who always played and struggled in IV as a "builder", who ALWAYS broke the cardinal rule (I always tried to build every last Wonder), who was the furthest thing from a warmonger - it pains me that Civ V should have been RIGHT up my alley.
Instead, what it's turned me into IS a warmonger... because then - at least I've got something to do beyond Next Turn my way to the next SP or what have you.