[karaterobot]

I'm suspicious of this: "the manager is considered incompetent but nice".

I'm suspicious because I immediately wonder who considers them incompetent. Is it their boss, is it everyone else in the organization, or is it just you? My point is that you have a particular lens on their performance, but you probably don't have a synoptic view of everything they do.

Of course, I don't know the details of your situation, but the hypothesis I'd test first is that they may be good at everything in their job description except the one specific thing you mentioned, which is that they're not communicating enough. If you talked to them about their communication, directly and unambiguously telling them how it is affecting your team, and what you expect instead, what happens?