I'm roughly in agreement with you on when the firing should have happened. Short of immediately after 63-0 (there was only 1 week remaining), there is no way that Smith should have been allowed to name himself as DC and elevate his son to coaching LB's that offseason. JW demonstrably failed in his oversight responsibilities there, and if LS would have fought him on those issues he should have been fired then. Either way, he should not have been HC without a DC and with an incompetent, nepotism hire at LB coach by the time the 2019 season rolled around.It's hard to assess how vulnerable we were to real roster devastation in March of 2016. That Cubit team was basically Beckman's, he got fired a week before the first game, it was his roster and his staff. Cubit had replaced most of the staff and was on a joke no-credibility contract. The 2016 class was weak and surely the 2017 even weaker, and how would the existing players have handled a year under a lame duck? And you also have to consider how absolutely poisonous the fan atmosphere was after Not Ideal. The relatively quality of the 2015 team does not tell the whole story of how shaky that situation was.
It MIGHT have been a better idea to ride out 2016 with Cubit and then do a real coaching search. But there are big potential pitfalls between March and December of 2016.
The problem wasn't the hiring of Lovie, which was a calculated gamble by Whitman from a position of weakness that he didn't create. The problem was the galaxy brained logic that prized "stability" as an abstract concept over really looking at what was happening. Not to mention Whitman's bad tendency toward structuring contracts to make it financially impossible to fire a coach early when he doesn't have to because he's not negotiating against anyone.
He should have been gone the morning after 63-0. That's the mistake. We've had some fun moments in the intervening two years, but we have a lesser roster and a lot of wasted time to show for it. And it would be worse if not for the Covid rules letting our seniors come back.