Off-topic: Always better to quote the earliest reference. Plato said practically the same think around 347BC. Maybe there was someone before him too when we had no written texts. History repeats itself.

I can only quote a known source. Though I won't be surprised if Einstein made that statement after reading Plato's.

Taking the bait: Why is it better? If one is attempting to persuade, I would suggest using the attribution that most strongly connects with the audience's sense of expertise and/or power. So, given that, I'd wager that Einstein is better reference than Plato for many in the modern world.

I get what you're saying, the idea is much older than Einstein but do you want to be right or do you want to be truthful and persuade?

Credit for originality.

At least nod the prior. "As Einstein's improvement on Plato's dictum says, ...".

By comparison, I was reading a paper on an alternative fuels process and found that its citations were all to 1990s and subsequent work.

This actively obscured the fact that the underlying concepts and idea dated from the 1960s, and excluded considerable significant prior research.

It would be ... like a study of evolutionary biology failing to credit Charles Darwin, and giving the impression, say, that the entire field grew out of recombinant DNA efforts of the 1970s.

I agree, though I find it likely the person you're responding to quoted their own earliest known reference :)