A few things to consider here, first WA fielded a very weak team this year, most players did exceedingly well against them, but even in that match Ellis didn't really take the game by the scruff of the neck like some of the other first round candidates. His kicking is generally neat but is often lateral or short, not to mention he often tries to be too clever and turns the ball over as a result.
Just going over his stats at TAC level, his KE was 49%, way too low for a player who has a reputation for elite disposal. For someone hailed as a strong mark, he didn't take one contested mark for the season, and his performance in the carnival was ok but not outstanding. He averaged 2 clearances a match, to put that into perspective, Blakely averaged 7.
There is absolutely nothing to suggest Ellis is worth pick 12, I would rather roll the dice on Cockatoo if all the others are off the board.