Heh, I would've agreed before the introduction of the XCOM Squad, but now, in the era I prefer to end games, a Domination victory is definitely feasible. I came close (experimenting with Portugal on King), but I ended up winning the Science victory before I could steamroll the rest of the world. Otherwise, Domination is horribly tedious and I just don't know how warmongers manage. Kudos to them, though.
edit: yeah, but some of us just don't like the attrition-slog through the civs, or we don't like it after a certain point. Even if it's only capitals, that can become difficult on larger maps