There is a difference between Lieberman and Heschel as Lieberman was exclusively known as a scholar who wrote on Talmudics.(actually Tosefta) His personal views on Torah, Mesorah and Halacha were less well known and clear giving him more room for those looking to accept him.
But as Rav Ruderman once put it when he was in his eighties and Lieberman who knew him from Slabodka (according to some they were roommates) wanted to visit him in the hospital, “No! The Alter warned me to stay away from that Bochur!!!”
Herschel, on the other hand, is even less of an anything in the frum world. No one has a hava amina of taking him seriously. His sociological view of Torah with some Greek philosophy thrown in does not give him a reputation as having been a person that anyone in the frum world has a reason to take seriously.
Of course, those who want to push the envelope in the frum world are going to claim that Leiberman and Herschel were these great Talmidey Chachomim who actually were 100% frum with a wonderful approach to Yiddishkeit that we should all respect. Um… in the 1950s the proponents of JTS said the exact thing and look where it got them.
For a change, I’ll actually with those who want to push the envelope in the frum world and say “stop these hagriophies!!!”