Fair points - cash wise they don't owe much more, so it's really just a matter of wrangling the cap situation (which isn't really all that severe). Agree with your point above about being preliminary with the extension though, as he was already making 64/4, which at an AAV is still the highest in the league.
I was thinking about it, and this extension was made to gain cap relief for their other players.
In a vacuum, I might say cutting him was the move, but easy to say from my office wearing slippers. SF has the issue of too many good players, there's no perfect way to do it. I probably would have sent Trent Williams on his way, but if he plays well till 40, I would have been wrong.
Even if, in hindsight, letting CMC go a year early was the right move, I don't know how many teams would have
actually pulled the trigger.