Explain to me what Monty's system was out there? I sure couldn't figure it out. Players looked lost on both sides of the puck, like they had no idea where to be. One game in and that looked much better. Yes firing the coach was the right move.
Monty's system was essentially more north-south movement, carrying the puck across the blue line, and sending forwards toward the crease for attacks in bursts. In contrast under Bruce and Claude there was more of a chip up the wall to get the puck into the attacking zone and using the cycle to attack with defenseman pinching to retain possession.
Defense had largely been zone box+1 throughout the whole time though they experimented with adding some man coverage last year IIRC.
I think Sweeney's roster moves this off-season brought in guys who would suit the Julien-Cassidy system more than Monty's. Elias Lindholm would be better cycling than freewheeling, he has good vision. Zadorov should be using his size to box out and clear the crease, not chasing around his mark. You've lost guys like Hall and Debrusk whose speed was an advantage under Monty.
Sacco can't reinvent the wheel overnight, but if they simplify and start valuing possession more and stop paralyzing themselves looking for shot quality in favor of just throwing it on from any angle and getting rebounds, results will improve. It's still not a SC roster but they can do better than this for sure.