Well, sure it is subjective no argument from me. If it were managed to be objectively processed and analysed we'd be in a different field entirely. But putting aside that it's hard to measure hockey IQ, I think the field of scouting and player development is changing. Sports sciences has enjoyed massive changes to fitness, rehab, injury prevention, diet and nutrition, etc.
The new gains on the fitness side has changed the field, so to speak, so I believe the differences between Player A and Player B have become MORE pronounced with those other things being more equal. Whereas before a highly skilled player who neglected his fitness could get by, I don't think it would be as easy for him to get to the NHL now when every player in this rich sport will be giving a 100% effort toward the things they can control and improve at every level, starting from atom and peewee. I think that leaves hockey IQ (or vision, or decision-making -- whatever you want to call the analytic mental side) as more important than ever. I'm not saying it's the magic ingredient but that many of the other ingredients are now more equal between the players than ever, leaving the distinguishing ingredients each more important than ever.
Inexperience is one thing, and it makes sense to give players plenty of time to catch up. No point in rushing a player to the NHL before he shows he's up to speed on his playmaking (hint hint). If a player has trouble processing the NHL-level game or has trouble adapting to the NHL-level speed, and he's been given ample opportunities and exhausted his options (like that Poolparty kid in Edmonton) then he doesn't have it - simple as. Close the book and move on. If you can't process the NHL game you'll never be a relevant player, you'll never be an impact player.
Now do I have any idea how to develop hockey IQ? No, not at all. Not one bit. My theory is that a player who is running the show on the ice in his current league and can play all situations should be given a shot in a higher league in a similar role (ie top6 to top6, not top6 to 4th line garbage minutes). This is what I would've liked to see from Kotkaniemi for instance. I really don't see the benefit of thrusting a teenager who is called 'a project' into the NHL as an 18 year old to play garbage minutes when he could be feasting on loads of minutes elsewhere, in all situations, against slightly slower, slightly worse defenders which allow him to figure out things on the ice by himself.