If no boob shape, then boobs squished.

Hi, lady here who owns and wears armor sometimes. There are a few things wrong with this.

(Prefacing that only a very very small number of women historically wore armor)

You'll find that basically ALL medieval plate bulges out in the chest. That is specifically because dome shapes are stronger, but also for ease of movement. A flat plate will make it harder to bring your shoulder back (or you'll need to make a bigger arm hole).

You'll also find that most people who do stuff while in plate armor tend not to carry a lot of fat, and since boobs are mostly fat, women who wear armor "for a living", and are thus swinging pole arms quite a lot, tend not to be very busty.

Thirdly, the main difference between my armor and the armor the guys are wearing is not in the plate, but in the padding underneath. I have a gambeson and armor coat that is thicker above and above my breasts than right in front. There's basically a boob-slot in the padding, so that a hit to my chest gets absorbed by my body instead of my boobs.