I really can't split them. Petracca is more mercurial in the way he can bust through an opponent/pack with pure strength, then break away and kick a goal. He's also got some freaky Daicos/Rioli moves. But Oliver is incredible with his speed, agility and vision. He is super aware of his teammates and is able to deliver the ball to them - sometimes faster than they can receive it. He always seems to be able to get his arms free and release a kick or handball. Now Oliver has added a kicking game to his arsenal, he's almost unstoppable. I think Oliver can win a Brownlow with his consistency. Petracca a little less consistent. Petracca has benefitted a lot from Oliver working in tandem with him - but that also goes in the other direction.
Most potent midfield duo in the league, being served by the best ruck duo in the league in Gawn and Jackson. We could win the flag next year at this rate!