What convinces me is seeing players who I identified as clearly below average decision makers making top players. Necas was one of them. Cozens is another. Newhook was a below average decision maker in the BCHL and he's still making a go of it.
Hockey isn't chess. You don't get a move, you have to take it, and you do so with speed, skill and physicality. To ruin what he's got you need to be like Podkolzin, Beaulieu, Liljegren levels of stupid. Absolute zero, head empty no thoughts.
With prospects, I think the IQ/decision-making concern has to do with making the right or optimal play rather than the clearest/easiest one -- this is because a player could be "cheating" and rely on his physical advantage against Jrs (most of whom would never make the NHL) to make a play that wouldn't fly in the NHL due to the smaller gap in physical abilities between the player and his NHL opponent.
Someone with a tendency to cut into the slot/middle to drive to the net for example -- just how valuable is it to see a prospect do that? I feel like the instinct to drive into contact is very valuable but the ability to bully the average Jr defender is not as much.
On the other hand, Lindstrom being able to play in the trenches is a translatable skill and a very valuable one. Ultimately, in high-end prospects I think you need to seek something from the the player that is
already on-track to better than median NHL-level because these high-end prospects are meant to improve the roster and bring a new element missing from the 20 man starting lineup, or the 6man top6 in this case.
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In terms of the names you brought up, I think a top5 player should have a prospective ceiling above that. I wouldn't use a 5OA pick on a player who tracks toward being Martin Necas or Alex Newhook (nor would I trade a 5OA for Necas or Newhook). We're meant to be aiming to pick up cornerstones and game-breakers.