My reference of placeholders only applied to Purcell, Schultz was "supposed" to be the solution and the organization considered him to be the solution until the point they didn't, I'm not sure at what point the org came to the conclusion they had more turd than gold in Schultz, but the conclusion was definitely something that was arrived at somewhere in the middle of this season.
Purcell was different in that I don't think he was ever part of the long term plans, which is why I think the term placeholder is applicable to him. In the absence of placeholders, what you are describing is trial by fire which is something we've had ample experience with and had a lot of player failure and team failure as result. It is good to challenge players, but it also important to put them in positions to succeed, you want to nurture their confidence and have them grow as players, there is a breaking point where it goes from challenging a player with just a little more then they are presently capable of and straight up drowning them at the deep end of the pool. The Oilers have done a lot of drowning in years past and I think we have scarred players and stunted their development as a result, I think if we had a 2 year placeholder instead of Gagner and kept Gagner in juniors, he would be a much better player as a result and possibly still on our team. Where I think we went wrong on our placeholder Purcell and the couple other placeholders we've had (we haven't had many) is that unlike Pittsburgh who knew Recchi and Guerin weren't part of the future of their core and would inevitably be replaced by younger players, they served as important mentors for their young core along the way.
With respect to Yak I really don't know what's best for him, he performed well under Krueger from an offensive perspective, but he was allowed near complete freedom out there and his defensive game didn't progress at all, his teammates also resented him for the double standard that was imposed with respects to how he was treated compared to the rest of the team. He also performed well under Nelson, but I'm not sure if that was cause of Nelson or just Yak playing well because he was happy to be free of Eakins. Yak really hasn't demonstrated that he is ready to take on a top 6 spot and there is a reason the org & coaches gave all the other young stars their spots with nary a hint of trepidation, but Yak has always been kept just outside of that spot. McLellan has given Yak a chance at that spot a couple of times and aside from his short stint with Connor he has dropped the ball, it wasn't long ago Pouliot found himself benched for taking stupid penalties and it was a great opportunity for Yak to show he was worthy of stepping up and he completely flopped on his face when given the role.