Agreed. All depends on tactics/ overall strategy. At the Storm, big Nelson doesn't play 80 at lock but plays as another prop. At Panthers, Yeoh plays 80 as a middle and link man (as does Murray at Souths). Countless examples of teams going either way. Listing Jake at 8 and Keppie at 13 simply says that Seibold and Flanagan want that extra prop in rotation.
As the season progresses and Gordie becomes eligible, Lawton back from injury, and both in great form, can see the possibility of using them with Croker as guys who can split their time between 9 and a mobile 13, maybe offering another point of attack through the middle in the same way McInnes and Finucane, and spelling Brailey at Sharks, sharing the prop, lock, and hooking duties.
At the end of the day, a middle forward is a middle forward. In the modern game, you will most probably require both types to be successful