Damian is no flanker. He lacks the power. You can't have a flanker who lacks punching power in the line.
As for Kolisi, what does he do well? He is a weak tackler, most of his tackles deemed successful on a stats sheet are tackle assist. These can be as little as putting hands on an attacker who is already going down, lending no stopping force. As per attack? He also lacks punching power in the line. He can be used as a link or cleaner with the outer pods. Usually grouped with a wing, Willie and/or 13. Line outs? A designated receiver. At the breakdown? Nothing. Can he pass? He does have some basic skills. No vision or ability to do much constitutively. His best runs have been on the seams, and very few of them amounted to more than a turnover. He has been lucky not to receive multiple red cards the past two seasons with his throat slams and spear tackles. He has no leadership either. Kolisi doesn't do anything very well. He is a big back masquerading as a forward. He could have been a centre. I'd say he is better than Damian right now. How good could he be? We'd have to see.