Taris was also bigger than any other area in KOTOR:1, so the size of Peragus doesn't bother me. And I think Nar Shadda on the whole may have been just as big as Peragus. Telos is also pretty big when you consider it's a space station, planet and underground.
Likewise if you count Dxun as an extension of Onderon, then that's a pretty big location as well.
With KOTOR:1, none of the planets approached the size or detail of Taris.