I don't always blame the QB - but it's clear that Goff needs near-perfect circumstances to be successful right now. And no, not every QB does - just take a look at Russell Wilson, Deshaun Watson, Brady, etc. The latter two have dealt with terrible OL their entire careers. Brady's WR group is mostly nobodies.
First of all, comparing him to Watson or Wilson is a non-starter. Goff doesn't have their mobility and never will, and that was known going in. And as for Watson, despite his mobility, he hasn't accomplished what Goff has at this point in his career. How many playoff wins? How many game tying and game winning drives in conference championships?
Wilson is admittedly great, but he has his down moments too. Seattle struggled for a few years. In McVay's first year, we went into their house and absolutely shellacked them, and Wilson was gawd-awful in that game. His performance has improved the last two seasons ... not coincidentally, so has his supporting cast.
Expecting Goff to be Brady at this point of his career is foolhardy. And while Brady hasn't always had great OL play in front of him, he hasn't had play as bad as we've seen this year either. No, he hasn't had terrible OL play in front of him his whole career, it's mostly been at least adequate, which you cannot say the same about the Rams OL this year, which has persistently been one of the worst units in the league.
As for your question on "if it's always supporting cast" it's pretty simple - some guys can't even do it when they have that. Recall that Warner took over for Matt Leinart in AZ, who wallowed in mediocrity. Warner took over, with the same supporting cast, took AZ to the playoffs three years running and to the Super Bowl once. Leinart could have never done that, and we know for sure because he had the chance with the same supporting cast as Warner.
Similarly we have seen what Goff has been able to accomplish when he has solid blocking in front of him and a decent running game to support him. He has neither of those things this year, and has a coach who, while I like him a lot, has had his offense figured out by the rest of the league. Maybe we should concentrate on fixing those things first before this franchise throws yet another promising QB under the bus.
If those things get fixed and Goff still plays like this year, I'll be right there with you in calling for a replacement. But this season, his offensive line has failed him miserably and the running game has taken a big step backwards, and thus I'm not going to target him as the primary culprit for this season's struggles.