3. We can see that many mechanics in Fcob are physics damage, such as earthshaker, bennu's straight line AOE. Parry is useful to mitigate those damage, too.
4. Multiple attacks to single target, such as Bahamut's claws. Parry is really useful that kind of mechanic , too.
Currently , I only found these advantages of parry.

For determination. I think it always is a good stat for tank. Since the new coil always request dps check, determination is really good to increase DPS for pushing boss before enrage or 3 bennus or bennus in T12.

In one word. I think both are really good stats. How to choose them totally depends on different players.