Heter? Keep in mind that the Gemara does not discuss this. The Nosei Keilim agree that Bedieved it is alright not to hear it yourself. Some say to do like the Zohar Hakadosh that the Beis Yosef brings. The reason we don’t simply Pasken like a Zohar is the same reason we don’t Pasken like a Medrash: because it is not any different than a Braissa. Just because we know that a certain Tanna holds a certain way, doesn’t mean we hold that way. The reason we don’t Pasken out of Sohd, is because we can’t work from that angle. We can never be sure that our understanding is the final picture. Just like we can’t rule based on Rav Hirsh’s explanations, and even the Torah’s own explanations, because we never understand the whole thing, as it says, “Rechava Mitzvascha Me’od.” When it comes to a discussion of how to Daven that Hashem will listen (sounds like a good title for a book), there is no reason not to listen to those who have a better perspective.
The Ben Ish Chai writes in certain places that if the Rishonim would have seen the Arizal they would have said deferently. There are times when we use our understanding of Sohd to be Machria in Halacha. It gives us a perspective of where things stand. When there is a Machlokes Tannoim, we see often that it stems from Svara, even when they quote Pesukim there is a reason why this one wouldn’t derive it from here and that one from there.