Honestly, having watched people argue about what simple is for about the last 10 years, I've pretty much settled on it not being a well-defined term. We know complex when we see it for sure, at least when it is present in quantity, but simplicity is not just the absense of complexity. There's at least three concepts we're all trying to stuff into the same word, and they are not only not "orthogonal" they are often in conflict with each other. I don't even think it can be rehabilitated, it can only really be abandoned, to clear the way to trying to characterize the multiple concepts we're trying to stuff into this one word.

It is especially dangerous when something is "good" and people try to appropriate the term to appropriate the goodness of the term, as if goodness flows from a term to the thing it is attached to rather than the other way around. "Simple" is good so my good thing must be "simple" to be "good". But it doesn't. Simple can even be bad, in the wrong place or in the wrong sort of "simple" for a given job.