As coach I'm not sure whether I'd pick Coates either. You might need to be training them to see their potential. At this point in the season, Walters has tried nearly everyone with Staggs, Piakura and maybe a couple of other combos and position shifts yet to come. The priority should be to win enough games to differentiate himself from the last atrocity. He needs to do that. The spoon again is not acceptable.
Coates is a prime example of a player who has not progressed under his watch. Just by his age and growing experience he should've improved the little complaints, like being out of position and spilling the odd high ball. The potential is there, more than any other winger in the competition (arguably, and certainly in the Storm's mind, who are good judges). He's big, quick and can leap like Cazaly, yet every complaint we had about him under Seibold's questionable tutelage has only galvanized under Walters. But he was a raw rookie then. That no longer stands.
Coates, himself, has openly rejected Walters coaching and turned to Bellamy to further his career. Next to undervaluing Walsh, that's Walter's biggest fail mark yet. Admittedly, the guy's judgement is no benchmark but it's one to put on the unfavourable side of the register.
Would I select Coates at this point in the season? I would if I thought he was the best chance of scoring tries and I thought I was making progress with his defence. But I would not drop him out of bitterness for leaving, nor would I drop him to learn in the ISC. I would want to milk the last drops out of him before he leaves. I would use him for what he's worth to me, not caring if it's good for his long term progression. Were he staying, my decision might be different.