words have different meanings; the root sense of 'simple' is 'one-fold', that is, only having one layer rather than two or four, and that sense is still present in phrases like the spanish hoja simple, meaning 'one-ply' (toilet paper, for example), but it's had multiple meanings for thousands of years including 'mentally disabled', 'honest', 'harmless', 'pure', 'unadorned', and, as you point out, 'easy'

it's true that using a word with multiple meanings gives rise to ambiguity, and avoiding that by choosing a different word is desirable

unfortunately there isn't a better term for 'simple' in the sense of 'not possessed of much detail' or 'composed of very few parts'; saying 'non complex' doesn't really help because 'complex' is often used to mean 'difficult' for the same reason 'simple' is often used to mean 'easy'

except in hucksters' advertising brochures, i don't agree with your implicit assertion that all the polysemic complexity of 'simple' is merely historical, leaving only 'easy' as a live meaning; i think all the meanings i listed above except for 'harmless' have some currency today, even merely in english

https://en.wiktionary.org/wiki/simple#Adjective lists nine main meanings of which seven are current, though i admit i just added the 'easy' one myself; it wasn't listed previously (i think because of confusion induced by the polysemy of 'complicated')