The cap management at the time of the signing was fine. UFAs like Tavares, a #1 Center, don't come along very often. You don't just ignore it. Kadri is a #2 center on an good team and #3 on a great team which do you want? Bozak is irrelevant, he wasn't a cap casualty, they has no intention of keeping him.
Biggest factors imo and 2 weren't necessarily fault of Management
1. The cap went flat. We wouldn't complain (as much) with 11m if they cap was around 100m like they were projecting 5 years ago. And anyone in management sports or otherwise, makes a 5 year plan. You could argue they should have adjusted on the fly, but they made a plan and stuck with it.
2. Only 1 of their young D developed into impact D (Rielly). 5 busts basically, Gardiner/Zaitsev/Dermott then Lilly/Sandin, Even if you blame the philosophy behind them, scouting & player development department went 1 for 6.
3. We would have done a lot of winning in the first 5 years so it's like meh, 2 years as an anchor wgaf
4. Imo the only deal they really messed up was Marner, which happened AFTER the Tavares signing, because of the Nylander holdout and how bad that season was, a Marner holdout would straight up burn a year of the window.