These are orthogonal concepts. Roman numerals can describe scale degrees and harmonic function in any temperament. They do not require equal temperament to "wo

These are orthogonal concepts. Roman numerals can describe scale degrees and harmonic function in any temperament. They do not require equal temperament to "work"; they work just as well in just temperament. The numerals describe the degree/chord's relationship to the tonic. The difference is that in just temperament, you cannot switch which degree/chord is tonic (Roman numeral I) without re-tuning, while in equal temperament you can switch freely. The Roman numeral notation did come a little while after Bach, but I believe the concepts the notation represents are older (though some of the concepts may have been more implicit in the past).