If you lose this way, it is your fault. That is why the land tile version of the Dom victory worked so well. You had to actively prevent it.
Moreover, it created global conflict. You had to worry about every settlement the enemy made, everywhere on the globe. You had to worry about any weak players with lots of land suddenly falling to an enemy and being gobbled up. You had to worry about enemy culture spreading quickly, allowing them to gobble tiles. It was conflict everywhere, all the time.
Most of all, you had to worry about losing. Because you very well could lose if you didn't actively prevent other players from grabbing tiles.
The "take the capitals" version of the Dom victory makes things much too easy. You only have to watch your capital.
I would be okay if they had both a "take the capitals" and a different "claim x% of tiles" victory. But that tiles victory needs to be in there. It was the source of all the conflict, and also explicitly made a lot of systems worked that failed in Civ V (in particular, putting an explicit premium on going wide and a need to worry about enemies growing too big).