Valuing systemic simplicity over simplicity of a feature in isolation is one view that gets me into a lot of disagreements.

Sometimes the simplest overall solution isn't so simple in isolation.

True enough. I think when we say “simple” we often really mean “cheap” (to maintain), so maybe it’s better to cut to the chase and just say that instead.

They’ll say it’s simpler (and better) if everything is a microservice.

It might be that they use simple in relative terms.

Linux could be considered simple given the problem it's trying to solve and yaml complex.

it's more often that they don't understand what simple means for most people

For example they might think that in a mixed-paradigmatic language the "pure functional approach" is more simple even if it introduces more indirection and requires a deep understanding of various more advanced language constructs(*).

Or that the simplest explanation of monad is the one based on PL-theory instead of an explanation based on terms people without an scientific-PL background are more familiar with.

Or people which think that writing down things in predicate logic is just way simpler then writing them down in English (well, I guess thats somewhat me).

None of the "I find this is simpler" points I mentioned are bad, but not realizing/accepting that what is simpler for you isn't simpler for others is the problem.

Rich Hickey has an excellent talk "Simple Made Easy". He points out that "simple" and "complex" describe objective properties. The terms are often (incorrectly) used interchangeably with "easy" and "hard", which are subjective.