While there's always the "derp derp arguments", there's also the possibility to push the reflection deeper, which is what people who lead and manage things do. I'll be using your post to provide the breakdown of Ottawa's season.
DJ Smith is a great guy with very good interpersonal skills but he's made to be an assistant coach. It was very clear that his systems were not working out (particularly in the DZ and NZ) but the Sens were STUCK with him (because they were stuck with Dorion) since it took so long for the TEAM SALE. Once that happened, it didn't take long for the new ownership to "get rid" of them without creating a PR mess. At the first occasion, Dorion was fired and DJ was also out after 26 games. All that said, the sale happened way too close to training camp, so unfortunately changes couldn't be made in the off-season (nobody would fire their GM and coaching staff in September)
DJ Smith 26 games, 0.423 P% (28th)
Even Strength
50.19 xGF% (17th)
46.63 SCF% (27th)
49.46 HDCF% (19th)
49.68 CF% (18th)
50.78 SF% (14th)
90.29 SV% (19th)
All Strengths
52.30 xGF% (8th)
49.04 SCF% (21st)
51.58 HDCF% (15th)
51.34 CF% (10th)
52.21 SF% (9th)
88.56 SV% (28th)
Jacques Martin 56 games, 0.500 P% (24th)
Even Strength
50.87 xGF% (12th)
50.60 SCF% (17th)
50.05 HDCF% (18th)
51.22 CF% (12th)
51.08 SF% (12th)
88.99 SV% (30th)
All Strengths
51.69 xGF% (11th)
51.52 SCF% (13th)
50.34 HDCF% (17th)
51.53 CF% (10th)
51.42 SF% (13th)
88.40 SV% (30th)
Now, it would have been foolish to expect an INSTANT change in the way they play after 300+ games coached by DJ Smith. I had marked down 11 games after the coaching change where I saw the biggest impact from the change.
After January 13th, 45 games, 0.556 P% (19th)
Even Strength
52.52 xGF% (8th)
52.00 SCF% (9th)
51.48 HDCF% (15th)
52.01 CF% (9th)
52.32 SF% (9th)
89.04 SV% (30th)
All Strengths
53.60 xGF% (7th)
53.60 SCF% (7th)
52.05 HDCF% (14th)
52.46 CF% (8th)
52.71 SF% (7th)
88.53 SV% (30th)
Conclusion : Sens were a much better team a few weeks after the coaching change, once the players started to "fix" their bad habits due to years of wrongful coaching. They were "gift-wrapping" goals against a lot less than before, unfortunately goaltending was even worse than before though.
Of course some will keep being controlled by their biases and/or poor analytical skills, but based on advanced stats, they were a top-10 team in the 2nd half of the season. Better goaltending and efficient coaching from the start, Sens would have been a playoffs team easily, despite Norris, Stutzle and Chabot health status
Personally, my narrative was that this team wouldn't go anywhere with Dorion and DJ Smith a few games into the 2020-21 season. Many Sens fans didn;t have any trust in Dorion since the Zibanejad trade and they were all right.