[Druby]

Mastery of Weapon Arts does not seem to be applying on Monk's Priest Staff. Mastery of Weapon Arts lists that it provides 15% extra STR scaling to any weapon that does not use STR as its primary scaling. Monk's Priest Staff is a Faithful Scaling weapon, with 50% STR and 70% Faith scaling, would I take to imply means it is a Faith primary weapon. Please let me know if I'm mistaken somewhere or if this is not working as intended.

[Rendar]

Mastery of Weapon Arts does not seem to be applying on Monk's Priest Staff. Mastery of Weapon Arts lists that it provides 15% extra STR scaling to any weapon that does not use STR as its primary scaling. Monk's Priest Staff is a Faithful Scaling weapon, with 50% STR and 70% Faith scaling, would I take to imply means it is a Faith primary weapon. Please let me know if I'm mistaken somewhere or if this is not working as intended.

Just because a weapon has more Non-Str scaling than it's other stats, unfortunately, doesn't make it Primary X weapon. There are 2 notable examples of this being the Handkerchief and the Howling Handshot, both being Primary STR at 20/30% respectively, but 70% san/SKI (respectively) scaling ontop.
Also, MPS is Stat Scaling - Faithful, Dextria-Light

Which is Faithful -30% Base, +40% FAI and Dextria-Light -20% Base, +30% FAI.

[Autumn]

Effectively, the first listed scaling is the primary scaling to put it a much easier to understand way, by default for Swords/axes/spears/fists/bows its STR. Any further scalings are scaling tags and are considered secondary, which is what Mundane would remove.