"Gen Yers lack confidence" without further qualification means "All Gen Yers lack confidence".

Gramatically perhaps, but in context these sorts of statements about the personal characteristics of groups of people are generally understood to be generalizations.

"Ravens are black" ==> "All ravens are black"

"Germans like beer" ==> "Germans have a significantly greater tendency to like beer than people in general, though of course there are some non-beer-liking Germans"

It could be an interesting question in linguistics to figure out the difference between the two types of "Xes are Y" sentence.