I don't think he was complaining about one being easier than the other, just that one gives fewer points than the other. It's true - due to the way the game calculates score, domination victories are much more likely to give you a higher score than cultural victories.
The military victories can be done quickly. They have no specific tech prerequisites. This means you can sometimes finish them early and get a massive normalised score. The peaceful victory types all require (either absolutely or in practice) certain technologies. Diplomatic victory via the AP has a very early tech prereq, it's true, but that's probably partly why that victory has been considered overpowered in the past. Building the UN requires a modern tech, space race requires loads of late-game techs, and cultural victory realistically needs music and liberalism, plus lots of time to pump out culture. You *can't* get these victory types early (other than the overpowered AP victory), so you can't get those massive normalised scores.
Domination victory entails having tonnes of land. This gives you a big score. Land helps with all of the other victory types (except maybe conquest, but let's focus on peacemonger ones), but it's not *essential* to have lots of land for those, and it can be quite difficult to do so. In cultural victory, grabbing lots of land can mean missing out on worthwhile wonders and delaying the construction of cathedrals. You only really need [number of temples req'd per cathedral on your chosen map size] * 3 cities. True diplomatic victories (the kind where people actually vote for you; not the kind that are domination victories in disguise) are often won as a fallback option when other victories look remote; at any rate, they're feasible for small civs. Space race victory does realistically need quite a lot of land (nowhere near as much as with domination though; you can't afford to have maintenance costs stifle your research), and you need to go further into the tech tree and hence get more points for tech, but it tends to come later than the other victory types, so your normalised score won't usually be high.
Basically, the score system *is* biased in favour of domination victories. You can score big with other victory types, but not to the same extent as you can with domination. It's not because domination is harder - most people find it the easiest victory type. A lot of people think cultural victories are difficult (almost as many as those who think they're boring...); I'm not convinced that's true anymore in BtS, but I certainly wouldn't say they're easy enough to justify the lowish scores they usually give.