yes, you can write off stats - or, to be exact, you can write off a particular interpretation of the stats. If player A has more rebounds (per minute) than player B, it doesn't necessarily means that he's a better rebounder. I can give you lots of examples if you want, and the same goes for assists. +/- is not even an individual stat.
The reality is that right now Moon has 0 offensive game, he doesn't penetrate at all, can't create his own shot, and his shooting is below average. He is extremely good in defence though, and in a way he's the opposite of Andreea. Rasho is competent in the low-post, not a major threat by any means - but we barely ever throw the ball to him there. Rasho is our best defender on bigs though, by a large margin.
So with Moon and Rasho you get tough defense and little offense. If you combine either one with Andreea, you would get a lot more offense, that hopefully will more than compensate. When we have moon and rasho together, there's almost no ball movement, even if TJ would feel like passing (he usually doesn't). With TJ, Moon and Rasho we have room for just one 3pt shooter, which makes CB's job a lot tougher.
And, if we play against a big center like shaq, yao, howard, we need rasho inside, otherwise we can probably do away with Andreea, because his weaknes on help D is overcompensated by Moon's ability to leap and block shots ...