This is true, I made a Dark Angel MArine and Got him to Level 5 to find out I only got a jersey. No full robe
You can take off the mark 3 chest piece and he will have the robe on his torso. To be fair you wouldn't see it anyway. The helmet part is true tho
eh, I'm willing to suffer a smidge of armor/robe clipping when the robes and Mk.3 chest piece create such a bad ass look.
Meanwhile, the Eldar sit in the corner, wishing for the tabards that all of the Aspects have in art and tabletop. But, robes are cool and you should feel cool when wearing one.