Correct! Tuning open strings (listening to an interval) and tuning by harmonics (listening to a unison without using frets) both result in a lack of equal tempe

Correct! Tuning open strings (listening to an interval) and tuning by harmonics (listening to a unison without using frets) both result in a lack of equal temperament if you eliminate the beating entirely. Only good piano tuners are really experienced in landing at the correct beat frequencies without electronic aid.