Your post says that you understand we botched his development, but I don't think you do.
1) He was brought up to the NHL too early
2) Had poor coaching under Kreuger
3) Had to play with poor supporting cast while
4) Suffered a major injury for the first time in his career
You can't possibly understand all of that and then flippantly look at his points and make a conclusion about his long term potential.
Flippantly? I'm going off 5 years of disappointing development and production, including his college time.
You aren't wrong on any of those points, but that stuff happens to most NHL players. Good ones find a way to still produce. At some point, it's time to put up or shut up for these players. Mittelstadt's time was this year....and he scored 19 points in 40 games. Why does he get unending string of opportunities and 2nd chances? His biggest ally is the fact that he's on a team that apparently is willing to punt another season and not invest in improving the team more than the absolute bare minimum, so's likely 'earned' a top 9 forward spot by default.
I think in an ideal world world, he would have spent another full year in the NCAA and two years in the AHL, so he'd still be on his ELC. But, we have to live in the reality that it's his 5th full NHL season this year and he hasn't yet produced anything approaching a scoring level forward in any consistent way. When do we say "It's not going to happen" for the him?