By Purim we follow the wonderful rule of:- “When in Rome, do as the Romans”.
Too bad this doesn’t work by Yom Tov Sheni.
If we were truly to literally follow Minhag Avoseinu beYodeinu:- bear in mind that a tourist at the Beis haMikddosh would have kept 1 day Yom Tov, since he would know exact day of Yom Tov, so a tourist today logically should be doing what our ancestral tourists would have done.