I don’t think being isotonic had any relation to how refreshing a drink is
Having the same proportions of electrolytes and water as the human body means that no electrolytes are passing through the cell barriers to establish such an equilibrium. Isotonic drinks tasting refreshing is probably just an evolutionary development to make us choose drinks that are easier on the body.
So I guess in a way, a low salt diet would be considered more “isotonic.” But solid food will inherently not be isotonic due to containing more carbs and amino acids than water.