I've seen huge differences in productivity between people who've been working with a given stack with for years vs months.
The quality just isn't even close. Recently I outsourced a project to two groups of people. A jr dev who had 2 years of experience but all of that experience was with the tech stack, and 2 sr devs (10 yrs experience) who had < 6 months experience with the tech stack. And the jr dev (who was an inferior dev in general) blew them out of the water because of the tech stack experience.
And honestly in terms of raw talent I think the sr devs were better, but it just didn't make up for the lack of tech stack experience.
The quality just isn't even close. Recently I outsourced a project to two groups of people. A jr dev who had 2 years of experience but all of that experience was with the tech stack, and 2 sr devs (10 yrs experience) who had < 6 months experience with the tech stack. And the jr dev (who was an inferior dev in general) blew them out of the water because of the tech stack experience.
And honestly in terms of raw talent I think the sr devs were better, but it just didn't make up for the lack of tech stack experience.