Stacked table column widths

Hi mhamlyn 

You’re raising very real and painful points — these are well-known friction areas when trying to build table-like layouts with Matrix/Table.
I also noticed that you opened an Idea in parallel — I’ve voted for it and will share it with colleagues as well.

That said, for some of the things you mentioned, there are partial workarounds that may help already today, depending on the exact use case:

Symmetric matrix column widths
In recent Power BI versions, when the matrix is symmetric, you can define column width relative to the matrix itself — effectively enforcing an equal-width distribution across all value columns, regardless of content.
This doesn’t replace numeric px input, but it can help achieve visual consistency.

REPT-based techniques
Various REPT-based methods can be used to control perceived width and wrapping behavior.
This video demonstrates one such approach:
https://www.youtube.com/watch?v=4ZtuifazEHk

Model-level formatting techniques
Some formatting and layout behavior can be influenced directly from the model (rather than the visual), which can improve stability when swapping fields.
Example here:
https://www.youtube.com/watch?v=twiwgEXy87g&t=8s

Table-focused custom visuals
If the primary requirement is truly tabular reporting, it may be worth evaluating visuals that are designed specifically for that use case, such as Zebra BI Tables or Inforiver.
They are paid solutions, but they provide significantly more flexibility for column control, layout persistence, and table-centric reporting.