284 piety with party buffs is a nice amount to have. At that amount you can cast your rotation without having to wait for mana, even if you had a bad mana tick i.e. mana tick after finishing B4.
I would not put piety on the relic since the stats on it grow with each upgrade, meaning you would have too much piety at some point.

I did read about it on reddit https://www.reddit.com/r/ffxiv/comme..._relevance_of/