Gallas is a very good defender, probably in the same region as Andrade. It's just that for Arsenal he plays wherever Wenger needs him, usually left-back, while he's stated several times he's a central defender. If Boumsong can play for Juve, Gallas sure as hell can.
Thuram sucks in the air while Andrade is adept, but Lilian is easily better with the ball at his feet. Gallas and Thuram are both about 1.83m and have approximately the same weight, so they have similar physical attributes. Andrade I would say is tougher than both.