It works, thank you! I was worried if it would still work on wavy text but it's fine.
Edge case : Anchoring it at Middle Center causes a weird thing. Every other line moves up and down trying to adjust offsets on every rebuild.
This is how it looks inside the editor when selected:
Rect transform is anchored at top left, integer positions, width 521, height 73 - constantly changes to 74,73,74,....
Inside the Super Text Mesh component the text is Anchored at Middle Center, and it's Centered. A quick fix I've found is setting the Base Offset y to 0.1, then Rect transform height changes to 72.9999 and the dancing stops.
Or just setting the Rect transform to also be Centered.