My worry with overhyped juniors is that in SL they hardly ever get rid of their flaws. Centre that can't pass? No worries, he'll learn it. Not. Winger that's useless defensively? He'll get better. Not. Halfback with no kicking or passing game? He'll develop it. Not.
Whilst Walker may "only be 19" he's also playing every week in first grade and doing well in some games and badly in others with seemingly not that much incentive to cut the bad and improve the good. Even if he never improves from where he is now he'll still get a SL contract somewhere. What worried me about the KR game and others before is the lack of urgency he showed - as though any time the ball moved more than 5 yards either side of the posts it wasn't his problem. That's nothing at all to do with ability.
I prefer homegrown players to signings but I can't stand rose-tinted views of homegrown players. Mind you I've got harsher as I've aged - it took me 5 years to decide Ryan Hall was actually pretty good.