Your point on Greenwood being a MID only based on 2018 is valid and he did have 74% time on ground that year. I'm arguing that he actually improved as a player last year considering he had less mid time and less time on ground and I'm using that season to project 2020. He might regress, which is definitely a concern.
Like I said though in 2019 that number was 52% midfield (I wrote the last post before I saw this response). I'll find the article where that is written. He is 27 and it's hard to trust a guy to improve at that age but he is relatively new to AFL after trying to be a basketballer, so its plausible that his skills are still improving. The aerobic capacity thing is definitely a concern, I'm hoping he can just get to above 75%. Based on how he played last year, I would say he definitely would have scored high 90's with 75% time midfield and 76% time on ground as he scored 85 with 52% midfield and 72% time on ground.
He may well prove me wrong. I struggle with these Boak late career "spike" type picks.