Goff had 2 really great seasons then went into the dumpster. Relationship issues between McVay & Goff seemed to be at the heart of the matter. What is unfortunate is that the Rams didn't get the best out of Goff and had to trade him when his value was in the basement. I think in the heat of the situation they may have lost sight of the absolute need to make the QB successful above all else. You offense won't be good unless you QB is rocking. I think Goff felt beat down by McVay and McVay lost confidence in Goff and things went into the crapper.
I think there is a little bit of fitting you plan to maximize the talent of your players with the QB being the most necessary. I don't think McVay who is a wonderful coach, was at his best in this situation. I sure both guys learned a lot from the experience and Stafford is a big upgrade but we paid a huge price to obtain his services.
Goff seems to have reclaimed his status as a good buy not great QB, a quality starter who has value in this league and is probably better than 1/2 of the QB starting in the NFL. Rams won a Super Bowl and have a better QB now. It has worked out for both the Rams and Goff so in the end it was time for him to go as the situation was unsalvageable.