The absolute minhag that people should have relating to mishing is to not mish arayn in yenner’s minhagim.
I have never heard of any Talmud Chochom or Godol who felt that not mishing an “over the top chumra”. In fact there are people who comport themselves that way the whole year.
And the minhag is not to eat food from outside the house, it is never purported as a reason not to have guests. In fact, I would venture that the people who are noheg not to mish have many more needy people as guests for yom tov than the people who proclaim that minhag is a stira to bein adam l’chaveiro and achudus.