I have always considered it somewhat paradoxical that we use a rigid piece of plastic to control a foots motion and then use a non-rigid (but firm) heel post to try and control the rigid piece of plastic .... my $0.02
I have often thought it odd that based on theory alone we think it is OK to try and hold the foot quite rigidly in one position when quite clearly the foot is a dynamic structure in it's entire evolutionary history.
I'm a bit of a fan of less rigid stabilizers, quite happy to replace EVA posts as required. I like to think that the foot can function into and out of the more efficient starting place we give it, rather than "lock it up and hold it there"
Regards Phill