Alternatives to "simpler is better"?

Less Is More, originally from the Bauhaus Movement in architecture and design.

https://www.lexico.com/definition/less_is_more

Less is more was the motto of architect Ludwig Mies van der Rohe, who advocated for minimalism. If you have something that is less complicated, that offers more in the way of results, easier for the eye and mind to process without added complexity and detail.

The corollary, that form follows function, meant never adding a detail (to the form) for the sake of decoration (which the function didn't call for).

Example in design: As the West looked to the East for inspiration, the Japanese concepts of simplicity in Shibui and Shibumi brought great appeal.

Example in writing: Editors often pare down drafts to eliminate words that don’t add value.

I personally feel that keep it simple is the simplest and most direct way of expressing the concept. This is the main part of what was expressed as a suggested alternative in a comment under the question: KISS. (But I feel that KISS might not be understood by everybody.)

I don't think it's possible to find something of this kind that could be a clearly better expression than keep it simple.

I also took the opposite approach.

I thought that in order to demonstrate something short as well as wittier and less direct (as clarified in comments under the question), I'd instead come up with a phrase that's actually complex, but which has a nice metre to it, and that, also in only three words, says to avoid complexity.

By it's very complexity, it demonstrates what should be avoided, so it's a kind of meta jest. I figure it's something that could get a laugh at (the right kind of) party after somebody has asked to have it explained.

Eschew anfractous dispensation.

I am using the following senses of the words, all from Merriam-Webster.

eschew:

: to avoid habitually especially on moral or practical grounds : SHUN

anfractous:

: full of windings and intricate turnings : TORTUOUS

dispensation:

3 a : the act of dispensing
        // the dispensation of medication
3 b : something dispensed or distributed
       // … one of the most remarkable cultural dispensations in the country's history, the        paperback book.
— T. E. Cooney

So, we have this:

• Keep it simple.
  
  → Avoid the distribution of things that are intricate and convoluted.
       (Distribution can be thought of as the opposite of keep.)
  
  
• Eschew anfractous dispensation.