As always, I think it is wrong to tar an entire generation with a brush like that. If you actually broke it down, you would probably find that there are segments that are doing well and segments that are doing poorly. And you absolutely should not judge an individual based on a sweeping statement like this.This is just an average and is kind of useless for most day-to-day interactions. I know from experience (my son and d-i-l and their friends are Gen Z for starters and we do have folks in that age group working for my employer) that there are lots of smart, hard working kids in Gen Z. They deserve to be treated as individuals, not put down for being "Gen Z". And lets be honest, boomers said crap like this about us in Gen X, Gen X has said it about millennials, and so on through the ages.
Does that mean there is no problem? Of course not. My experience is that our education system and methodology is kind of f-d up, esp. where fields requiring the rigor he talks about are concerns (e.g. math). My daughter-in-law is very unhappy with the quality of students she is getting as a TA in university. But assuming that everyone in a generation can be judged by the average is just as "dumb", IMHO.