I think you are all right in your doubts about Byrne. He will play mainly Fwd pocket, and he will struggle to get any consistent/meaningful on ball time.
This is obviously a bad thing when playing for a team like Melbourne, who struggle to get the ball into the Fwd50, let alone use it well when they do.
I like Byrne, and he will 90% likely be in my team for 2 reasons.
In the reasons against, that I stated above, it would seem to indicate the ball will spend a lot of time on the ground when in the Melbourne Fwd line. The upshot of that is, if you have a Melbourne Fwd, is that he should be a smaller player.
Secondly, in the abscence of any obvious Zorkos (16/100), Treloars (18/83) or Adams (15/75), picking a Fwd Rookie that will play more than 12 to 14 games, and average better than 65 is like playing lotto. With Byrne, even though you are paying twice the price, I think you are getting good JS, and he should be able to average at least 70.
Does he have the potential growth of a lower priced Rookie? No. Is he likely to get to his Milking price quicker than a rotated-in-and-out-of-the-side Rookie? Definitely. Does he have a potential upside, to average more than a satisfactory 70/game? Undoubtedly.
He's in for me, at this stage.
oh, and p.s. WandP answered the question I intended, but I was intrigued by others take on it