Not really all that underrated I dont hope, dude is solid and the "rightfull" BW champion.
If Cruz comes back for Barao as his first fight then I think this will be one of the times when the real champion will be an underdog. If not I'm going to make big paper.
As someone pointed out, Barao probably is a bit in the shadow of Aldo, which might be why less people care about him, but in the end the lower in the weightclasses you go, the less people care. It was like this with the LW guys for the longest time till it broke through, I'm sure the lower weightclasses will aswell once they start to stack.