Younger generations and (large) cities - could this actually *hurt* Democrats?

[All Along The Watchtower]

What I mean by the thread title is the tendency of young, college-educated, and liberal-minded people to congregate in certain, mostly large cities/urban areas. This is true for people of this description from every region of the country (or of the world, in many cases these days), for both men and women of this description, people of all ethnic and racial groups, as well as both LGBT individuals and those who are straight/"cis", and furthermore, people who don't belong to (conservative, white) Christian groups, or who are even religious at all. And all of these categories overlap in significant ways, of course.

The implication here is that the places where all of these younger, largely liberal/left-wing people move tend to be already overwhelmingly Democratic areas, and are more often than not in pretty safely Democratic states, so if anything, this trend is getting stronger. This obviously already hurts the Democratic Party in down-ballot races, but I'd argue it hurt them in the most recent presidential election as well. And in light of Republicans currently controlling the governments of a lot of "purple" states - which has lead to both egregious gerrymandering and even more egregious voter suppression efforts - as well as the younger generation continuing to lag behind older Americans in registration, turnout, and broader political participation (for various reasons that would take another, longer post to adequately cover), I'm seriously wondering if these demographic trends that on the surface do indeed look very friendly to Democrats might actually hurt them, if only in the short-to-medium-term.

Curious as to what others' thoughts are on this topic.