On the other hand the idioms identified point to a long-standing understanding that sometimes, they are in conflict; a corollary of which is that one who always chooses complete honesty has likely failed to be polite from time to time, and one who is unfailingly polite has, like the curate describing his egg, likely given less than the total truth.
Most of us tend towards the politeness side of the tradeoff - we might, for example, describe a potential process failure when a more honest appraisal is that carelessness was the root cause.
I was reacting to @stemc43 who said "I'd rather work with...". Why wouldn't you rather work with kind and honest people? If you are picking your ideal scenario already anyway why not pick the positive version instead of the negative one?
But we all know all that has nothing to do with honesty, it's about political control, in and outside a informal community. Open source is defacto an easy target since most projects don't have real organizations. The people who pull these stunts in the open source world have no power of persuasion in private businesses, they can't impose their dubious code of conducts,contributor covenants and other "post-meritocracy" manifesto there.
In other words there may be much fewer people who are truthful, kind and technically skilled at the same time.
If kindness were constant among people we wouldn't say that some people are different.
If kindness is trainable and important, why is it not taught in schools?