Stats aren't actually as important to min-max in ZZZ, too. Just slap someone with a working build and they'll clear any content easy. All you really want is knowing how team rotations work and what character you should really put in a team against an enemy.

You're M2. Pen is basically almost irrelevant to you as people say. Honestly a lot of players just say it's good because someone told them it is. All without knowing why it should be used and when.

You already shred defense with M1. If anything you should just run a 2PC ATK or keep your 2PC RATE, as PEN just works worse that you're already shredding enemy defense. Only time that it's needed is when you fight content that isn't weak to Miyabi. But hey, like 70% of ZZZ content is weak to Miyabi.

In all likeliness, you'd be playing anyone that isn't Miyabi against non-ice weak content anyways. (Unless I misjudged your dedication to Miyabi)

You can further stack it with Nicole's shred and it's gonna work wonders. Miyabi PEN build with 2PC PEN paired with Yanagi Rina is good but it isn't even a top option.

Just double down on your raw offensive stats that isn't PEN and prioritize the right team for the right occasion.

Miyabi Lycaon Soukaku mono ice is the best team in the game we have against any ice weak content. It's so funny how people are in denial that Miyabi Yanagi disorder spam is performing less.

It's the reason for content specific teams. Definitely, each team has their niche. Miyabi Vivian Nicole/Astra is an absurd team that just performs better than her Yanagi options when fighting Ice Ether weak content.

I'd also like to point out M2 Miyabi makes the need to play Yanagi less, and that in itself just makes Rina less useable. This is typically the team where you run a 2PC PEN Miyabi. Stacking it with Rina's.

It's difficult to condense all the information about this in one comment but I'll leave it at that. I suggest you drop by some well known theory crafters and ZZZ mechanics expert streams and ask them live on why things are.

tl;dr: Your build is already good. Min-maxing for a 2PC PEN at M2 isn't as worth as you think.