Warrior of the Mystic Arts (UA)

I think if the idea was to actually make the lvl 17 capstone useful, it needs to actually provide the following:

1 - It must actually allow you to gain some form of advantage in terms of action economy (like casting a spell and getting to attack in the same action)
and
2 - It should actually utilize Focus Points, since apart from generating spells slots, NONE of the subclass features of this subclass actually do that.

Personally, I would go for something like this:

"When you use the magic action on your turn to cast a spell of level 1 or higher, you can pay an amount of foucs points equal to the level of spell slot used. If you do, you can make up to two unarmed strikes as part of that same action."

And yes, that is quite the power spike compared to the previous one, but it think it would be ok, especially when comparing to the lvl 17 features of other subclasses, like mercy or Open Hand.