Yeah, Goff struggles under pressure. He lacks a certain type of twitchy mobility that could give him an extra advantage but I don't think this is all on him. This offense was initially designed by McVay to depend on a power run game that gave him the advantange in play-action. These plays tended to involve long developing routes with Goff having the extra time to make great medium/long throws for big gains. ( I was always struck that, while coming from the Gruden tree, I thought the O was more similar to the Coryell/Zampese line.)
When the run game suffered and defenses adjusted the passing game suffered. It has taken McVay and staff almost a year's time to readjust to these realities and it's been a painstaking experience for the whole team. The adjustment has been successful, IMO. Like many others, Goff had an off year replete with pass passes at bad times. It happens. I think the plan B at QB has already been in progress. Knowing he's not quick or twitchy, but can run and see down field with his height,
McVay has finally found an answer (while the young O Line is building and growing) at QB. But it won't be complete until the running game becomes explosive again.