Make, learn and talk about needle lace.
Your example is actually quite well done. My first was far worse.
I think the nip-in-the-waist in the 3rd segment has occurred, as you suggested, from too strong a tension in the lace filling stitch. Your stitches are evenly spaced, but buttonhole stitches do have some elasticity. Tension solves that problem. It takes practice.
In your 4th segment, if it were me, I would have spaced the buttonhole stitches closer together. In most cases that corded buttonhole stitch is worked much closer together, much more dense. In the way it is used, it corresponds to cloth stitch in bobbin lace.
But in modern needle lace, we do what pleases us. So please yourself in spacing etc. Lace design is about juxtaposing different textures, different densities, in a pleasing way. In lace, although we modern lace makers often use color, texture and density differences provide the eye appeal, instead of color.