It's a unicorn.
And now there's no need to sew anything else ever.
I adjusted the darts big-time - moved them, made them smaller, and shortened them. Then I eliminated the gap at the neckline, adjusted the curve of the armhole to accommodate my slumped shoulders, and changed the angle of the shoulder seam.
All these small adjustments worked! I also sized up to a Medium - because I am a medium up top - and the final result is a perfect fit!
Matching the plaids was tedious, but I focused on the front matching and the bottom sides -- they did, but it took every bit of my fabric.
Pattern: Made by Rae Washi dress
Fabric: Kaufman 1" Carolina Gingham from fabric.com
Changes: Alterations detailed above
Verdict: After 10+ years of sewing, I finally have a garment that checks every single box. Woohoo!