Really great post~! ^^ truth is I been doing a little playing around with this same thing starting a few days ago after I decided to get back into lancer again. Most of my results are similar to what was posted here. With a 293 STR, 581 AP and 236 Piety. 290 seemed to be the cut off point completely for STR and I had no real difference minor or major going from 290 to 293. Once we are allowed to readjust stats am going to swap somethings around a bit more to boost my piety up a chunk I think just because of what you said here.
I often solo a lot or do off tanking during parties and a lot of times my survivability in these situations depends on being able to land those heavy stuns sooo forgoing piety completely or putting it as a after thought worries me a little~.