Sorry....but you're overstating how bad Garoppolo's supporting cast is.
George Kittle is an excellent all-around TE, and the 49ers have a very solid committee of RBs in Tevin Coleman, Matt Brieda and Raheem Mostert. They shredded through the Aaron Donald-led Rams defense last week and have the 2nd rated rushing attack in the NFL.....so their O-line can't be that bad either.
And behind it all....Kyle Shanahan is an excellent play caller, as well.
They're also #2 in total defense.... #1 in pass and #6 in rushing.
I can see why one might give the nod to Garroppolo at this point but I don't agree that there is THAT large a degree of separation in talent and capability between he and Brissett....and Jimmy G is hardly the only reason the 49ers are 5-0.
For me....Brissett is in the "wait and see" category....so the balance of this season will tell us a lot.