Yes. If I could rewrite mine I would lead with that rather than with the grading mechanics.
Ola
@grade_the_line
Blends between sizes with a pencil and a curve and finds it less scary than it sounds.
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It is what you should have been doing, and it is far less advanced than the word suggests. Grading between sizes is drawing a line from one size to another. That is genuinely it.
Why your current approach fails is worth stating, because it explains the frustration: cutting the largest size makes the shoulders and armholes bigger too, and those are the two things a tailor cannot easily fix and the two things that decide whether a garment looks right. You have been sizing for the easiest part of your body to alter and compromising the hardest.
The method:
Cut the size that matches your bust and shoulders, because that is where the unfixable structure is.
On the pattern, mark the size you need at the waist and at the hip on the relevant lines.
Draw a smooth curve between the marks, moving gradually rather than stepping out. Blend over a good distance - from under the arm down through the waist to the hip, so there is no corner.
Do the same on front and back, and check the side seams still match in length.
That is the whole technique. A pencil, a ruler and a curve, and it takes ten minutes.
The result fits at the shoulders, which is what everyone notices - and has room where you need it.