The issue is that every coach who plays a specific system automatically produces a set of diminishing returns. As soon as other teams scout and analyze his system, they can exploit it - and if he remains rigidly attached to it, then his team is easily picked apart on the ice.
Now, I don't know for sure if Tippett has stuck with "his" system the whole time he's been here or what, but common sense indicates that both the familiarity of how the Coyotes play along with the increasing ease with which opponents exploit us are signs that either his system or his coaches' have lost their effectiveness. Remember when Newell Brown took over the power play? For a while it was the only thing we were doing really well, but over time it has steadily diminished in effectiveness.
Tippett keeps talking about execution, execution, execution. Well, even the most perfectly-executed system is prone to exploitation if the other team can predict and adjust for it. Domi and Duclair prospered the most last year when they went "off-script" and let their innate talent dictate the play. I think that if we really have good prospects in the system like everyone tells us we do, we need to give them freedom to create plays rather than force them into a tiny shoebox.