Just turned the computer on to find “vochindik”‘s long essay on the sholosh shevuos. He tries very valiantly to describe the “sholosh shevuos’ as halacha, from out-of-context excerpts of Igeres Teiman and the Maharal and others. All I know is that halacha is codified in the Rif, Mishnei Torah, the Tur, the Shulchan Aruch and nowhere,absolutely nowhere, is there even mention of the sholosh shevuos as being normative halacha. So, you ‘ll just have to forgive me if I take your sources very skeptically and will not take an aggadah as indicative how to interpret halacha.
Additonally, plenty of Poskim have demonstrated pretty conclusively that the sholosh shevuos have lapsed, for many reasons.
Lastly, and this brings the argument full circle, if it was such a big sin, why were the great bulk of jews who perished in the Holocaust just those jews who espoused the sholosh shevuos and those that ignored them (by moving to Eretz ysroel) were saved?