Ah, so almost all nationally respected NFL experts and talent evaluators (including ex-players), all have a left wing political bias for some magical reason, even though pro sports and NFL fans generally skew conservative. Wow, that is identical to the creationists who say that all scientists have a left wing bias to favor evolution. It couldn't possibly be b/c they are experts and the evidence clearly favors that conclusion.
You could also just look at the objective stats yourself, but I guess math and numbers are also too "liberal" for you.
The guy was benched for Blaine Gabbert. Twice. When you've gone lower than Blaine Gabbert there is not much lower to go.
He didn't go lower than Gabbert. He was benched by failing coaches of a terrible dysfunctional team with no supporting talent and among the worst O-line and defense in the NFL. Also, Gabbert was benched for Kaepernick in 2016.
In 2016, Kaepernick had a 91 passer rating, a 4:1 TD to interception ratio, and had rushed for 470 yards in just 11 starts.
His rating was better than 13 of the 30 QBs who started at least 10 games that year, all who all have started in the 3 years Kaep went unsigned, with several of them signed by new teams during that period. His rating was also better than 7 of the 9 QBs (including Gabbert) who started fewer than 10 games but threw at least 130 attempts. And none of that factors in that Kaep was playing with teammates and for a coach who were objectively worse than all other QBs had to deal with, yet he still did better than them on an individual level. SF's defense was the worst in the NFL, it's O-line among the worst, and a group of no-talent receivers and running backs who fumbled more than any in the league (they had traded their only other playmaking offensive player, Alquon Boldin).
And again, the NFL knows this and knows your claim he was no good is absurd, which is why they settled. If he was objectively as bad as you claim, it would have been a cakewalk defense.