An "underperforming" worker can consistently underperform though, and that consistency might make people feel good. Ultimately you're right on a deep level, but perhaps there are other ways to produce good feelings than what you've suggested.

The recency of the good feelings matters too. If you push back now and set expectations for everyone, then a year from now your boss will probably remember the consistency more than the push-back.

Of course, it will depend on the people involved.