I'm not disagreeing as much as I'm trying to understand your point of view. Essentially, if I understand correctly, you were resigned to the 49ers kicking a 55ish FG with like you said, a 50/50 chance of making it. 50/50 chance of losing right then
The only difference between that, and what McVay did was assure the team that the Rams would have time left after the kick, whether it was made or not.
We also will never know if Shanahan would have called timeout himself after the Deebo catch, but that's besides the point