I reckon Marshall has had a more influential year than Gawny and according to footywire comparison (link below), Marshall betters Gawny in the following categories
Disposals, goals, tackles, goal assists, contested possessions, effective disposals, disposal efficency, marks inside 50s, clearances, centre clearances, stoppage clearances, metres gained.
The rest of the stats are break-even or Gawn slightly ahead (with the exception of hit-outs 28.5 to 39.4).
Interestingly, against Grundy, the story is quite similar albeit Grundy slightly more ahead in more of the categories but as with Gawn, hitouts are the only area he is more dominant in (28.5 to 41.3).
https://www.footywire.com/afl/footy/ft_ ... 1=S&fid2=S
https://www.footywire.com/afl/footy/ft_ ... 1=S&fid2=S
So all in all, I would have Marshall as the 2nd-best ruck in the comp therefore he should certainly be in the squad of 40. Either way, Marshall is younger than both of them and I reckon has way more upside given the fact that he is a natural forward. He's easily become my fave Sainter!