I have absolutely no "superhero fatigue" (which I don't even believe exists anyway), and I liked the first Shazam film and I still hated this one. Ignoring the fact that in between films its come out that Zachary Levi is a fairly detestable person, I just thought that the movie was poorly written, and neither the heroes or villains were particularly compelling.
In contrast I really liked Black Adam. Outside of the teenager (who could have easily been cut) I thought it was a very solid movie, not as good as TSS or WW1 but probably about as good as Aquaman (in different ways though, because they're very different films).
I think that Shazam 2 suffered more from the first movie not exactly setting the movie going audience on fire, and DC movies in particular having developed their particular reputation.
