That’s funny because I had the exact opposite reaction. In theaters I couldn’t remember anyone’s name and didn’t find anything compelling about anyone other than Chirrut, Baze, and sort of Krennic. Since then I’ve grown much more attached to the other characters.
The problem with Krennic is that he’s a weak villain and gets weaker and weaker over the movie, while Chirrut and Baze had no reasons to be in the movie, since they’re not even connected to the plot at all (they’re also the cliché-ridden tragic homosexual couple). One of the problems the Disney movies have (IMO) is too many characters at the same time, which makes things more confusing and/or bloated. Remove Chirrut and Baze and Rogue One gets better.
Krennic works well as the guy who is losing power. it makes him desperate. I don’t get your complaint that him getting weaker is a problem.
My problem with Krennic is one of dimension. He’s kind of an over the top bad guy. The bickering power struggle with Tarkin gives him a second dimension. The problem is, though there are hints of a third dimension in his first scene with Galen (where he implies the Death Star is justified), it never crops up in the rest of the film.