Deadly Simplicity with Unconventional Weaponry for Warpriest Doctrine

Question

I'm trying to figure out if Unconventional Weaponry makes Katanas work with Warpriest features but its looking like it doesn't.

The Warpriest Doctrine says:

If your deity’s weapon is a simple weapon or an unarmed attack, you gain the Deadly Simplicity cleric feat.

The Deadly Simplicity feat does this:

Prerequisites deity with a simple or unarmed attack favored weapon, trained with your deity's favored weapon

When you are wielding your deity’s favored weapon, increase the damage die size of that weapon by one step.

The deity Shizuru has the favored Weapon Katana which is a Martial Weapon.

The Human ancestry feat Unconventional Weaponry does the following:

Choose an uncommon simple or martial weapon with a trait corresponding to an ancestry (such as dwarf, goblin, or orc) or that is common in another culture. You gain access to that weapon, and for the purpose of determining your proficiency, that weapon is a simple weapon.

Since the weapon is only considered a simple weapon when determining your proficiency. So:

1. You would not get Deadly Simplicity for free through Warpriest since the Katana is not inherently a simple weapon.
2. You can't even take Deadly Simplicity as a feat at all.

Does this sound correct?

Answer 1

You can't increase the die of a Katana with Deadly Simplicity

As you wrote, Unconventional Weaponry only makes it a simple weapon with regards to proficiency.

Clerics are trained and become expert with their deity's favored weapon anyway, so neither Deadly Simplicity nor Unconventional Weaponry gives you any benefit.