Sure, over the long term 'lump of labor' is clearly wrong.
However, that does not mean that those displaced from work will not struggle to find new jobs. You're not going to turn most coal miners into coders. There's also no guarantee that you replace automated jobs with better jobs. Much of the service sector work that's been created in recent years has been low wage.
TLDR: Just because there will still be jobs, does not mean they will be good ones or that the workforce can easily shift to them.
However, that does not mean that those displaced from work will not struggle to find new jobs. You're not going to turn most coal miners into coders. There's also no guarantee that you replace automated jobs with better jobs. Much of the service sector work that's been created in recent years has been low wage.
TLDR: Just because there will still be jobs, does not mean they will be good ones or that the workforce can easily shift to them.