Rich and lean are relative concepts, not absolute. You can pick your reference point. It could be:
rich/lean of stoich
rich/lean of best power
rich/lean of peak egt
or simply rich/lean of the intended mixture.
Certainly rich and lean are relative but the only “reference point” in that list that isn’t arbitrary is stoichiometric. That is because stoichiometric is the mixture where there is physically neither an excess of fuel nor an excess of air. It is an equivalence ratio of 1.
The point is, there are rich and lean mixtures. it is incorrect to say “all mixtures are lean”, which was what I was responding to.