Artistic interpretations were based on ideals, not reality. And there were plenty of Renaissance painters who painted traditional dumpy folks. They were learning about the body, anatomy, about "self" idealization as opposed to religious idealization...in reality they lacked a variety of nutrients and were shorter...not bigger. The farm-hands probably were ropey and muscular and probably had good stamina, yes, but they probably also had a good layer of fat on them too.
The rich were regularly painted as fat and slovenly unless they were actually patronizing (paying) the artists to - again - paint idealized versions of them. The rich were often lazy and gluttonous, the poor were malnourished and overworked. No one looked like the statue of David.
But they also didn't have modern medical advances, serious information about nutrition, etc. - the majority of folks were in poverty and often sick, lacking basic understanding of viruses and bacteria. Infant mortality was high. Lifespans were low...this chart only goes back to 1800!
Of course, this varies widely depending on what age you talk about. The Renaissance is not really "ancient". Talk about Ancient Greece where most food was meat and olives and people were constantly at war...?
Right now I think we have the best of both worlds available. Knowledge and the ability to put it into action.