My only success against Obliterator happened when he stuck in for like 10 rounds.
He didn't drop ANYTHING. Not a single pillar.
By the time he dropped some earth pillars, i got quicksand/pulverizer.
By the time the he put the first shrieker, i had Oty.
And by the time he used gravity force, i got more than one Oty
So, he can be sometimes extra easy, but most of the times stomps me out in 5-10 rounds.