The related question refers to the view that those outside Israel need a second day Yom Tov in order to achieve the spiritual status that those in Israel can achieve in one day
It is expressed here like this:
בכל יום-טוב שורה בעולם גילוי רוחני גבוה. בזמן בית ראשון היו לבני ישראל נשמות גבוהות, שיכולות להכיל בבת אחת את הגילוי הרוחני הגבוה. כאשר חרב בית-המקדש השפיע הדבר לרעה על היכולת הרוחנית של הנשמות, עד שהן הגיעו למצב בו הדרך היחידה שהן מסוגלות להכיל את הגילוי הרוחני שבכל יום-טוב הוא על ידי שיתחלק ליומיים. וזו העילה הרוחנית לכך שהשתלשלו הדברים כפי שהשתלשלו, עד שנולד 'יום טוב שני של גלויות'.
In the times of the 1st Temple the emanations of the Yomim Tovim could be received by people with their elevated souls in one day. After the destruction (and the exile) the only way to contain these emanations was to divide the day into two and this is how the second day of Yom Tov came about.
My question arises because of the Gemoro in Beitzah 4b
וְהַשְׁתָּא דְּיָדְעִינַן בִּקְבִיעָא דְיַרְחָא, מַאי טַעְמָא עָבְדִינַן תְּרֵי יוֹמֵי? מִשּׁוּם דִּשְׁלַחוּ מִתָּם: הִזָּהֲרוּ בְּמִנְהַג אֲבוֹתֵיכֶם בִּידֵיכֶם, זִמְנִין דְּגָזְרוּ הַמַּלְכוּת גְּזֵרָה וְאָתֵי לְאִקַּלְקוּלֵי.
The Gemara asks: And now that we know the determination of the first day of the new month, what is the reason that we observe two Festival days in the Diaspora? Because they sent a warning from there, from Eretz Yisrael: Although now there is a fixed calendar and there is no uncertainty, be careful to observe the custom of your fathers that you received, because at times the monarchy will issue decrees of persecution restricting Torah study and the fixed calendar may be forgotten. And the people will come to have their proper observance of the Festivals be disrupted again.
This Gemoro implies that the people in Bovel sent a question to those in Israel asking about observing 2nd day Yom Tov seeing as the original cause for the second day which was uncertainty as to which day was Yom Tov had now gone away with the use of the fixed calendar. The response was to to observe the custom of your fathers that you received for the reasons stated.
It seems like the people in Bovel did not feel that they were missing the emanations in only one day. Further the warning that came back from Israel did not mention this point of being unable to get the emanations in one day.
So my question is how does the view that people outside Israel must have two days Yom Tov for spiritual reasons fit with the reason given in the Gemoro in Beitzah.