I’m not going to debate Liebermann or Heschel. End of the day they cast their lot with the conservative movement. (Now their opinions aren’t valued even there…)
Liebermann was childless. Heschel did not raise his only child (daughter) to be a frum woman.
Given the circumstances they faced and the situation they were in only Hashem can judge them as people and as Yidden.
But one thing is certain. There is absolutely nothing the frum world should be turning to those people for.