He did specify "in the long run", which I think is probably true as the timescales get longer. I doubt anyone would argue that humanity would live lives relatively unchanged from the present say, 3000 years from now. So it's really just a matter of arguing about 'when' and not 'if'.
I'd also like to point out that although we didn't "become" the assembly line, employees certainly have become more replaceable in many of the jobs impacted by the assembly line. Depending on the job, some employees have become the metaphorical "cog in the machine", and can be replaced by other employees with minimal training, as compared to the artisan-based system that predated mass production.
I certainly see your point, however, and I truly hope that we can maintain our liberty and humanity as technology increases, instead of regressing into a kind of dystopian neo-feudalism.