The meme is that his system worked for 1 year regular season only, and after that has been a complete trainwreck as soon as teams learned "oh wait, they only play a perimeter game? LOL".
Anaheim destroyed it in that first season playoffs.
The next couple seasons, playoff teams caught on but not the bottom-feeders.
Last year, the middle of the packers caught on.
And this year, even the bottom-feeders mock it.
And now, based only on observations of Thornton's play, I think he's checked out. He's sacrificed a lot of his offensive game to play a more complete 2-way game and it hasn't worked for him. TM also designed the system around JT, but I still think JT's just done with the current setup.
Which is why a move to an interim coach makes so much sense if management wants to make the playoffs. Trading young assets away now to try and push for a 1-and-done playoffs would be a "fire me" move, when you could get better results from an interim coach change (IMO).