Using the same settings on UI Text and TMP Text with the same font (using Roboto Regular) with Auto Size disabled produces the same results (as far as I can tell) with any point size. See image below of the two using the Scene B you provided using point size of 200.
The super subtle grey outline around the text is UI Text.
Changing the point size of UI Text or TMP Text will affect the Preferred Width of those text objects which will affect their RectTransform width. Below is an image of UI Text and TMP Text using 150, 275 point size where you can see how this point size affects the Preferred Width and RectTransform width.
As you can see the results are virtually the same which produces the same layout results. The RectTransform width is driven by the Preferred values in both cases.
Now when using Auto Size / Best Fit, we do have a key difference where the Preferred Width reported by UI Text will be based on the point size of the text object as opposed to the resulting point size of the best fit.
By contrast, the Preferred Width reported by TMP will be the optimum / resulting point size of Auto Size.
In the above image, both text objects have a point size of 0 with Auto Size / Best Fit range of 0 to 300. In both cases, the resulting Auto Size / Best Fit ended up being 300 points. However, in the case of UI Text, the reported Preferred Width is 66 which is no where near the actual width of the text at this 300 point size. This is incorrect in my opinion. By contrast, TMP text object reported Preferred Width is 1257.19 which is exactly the width of the text object at 300 point size.
Back to your reproduction scenes, since your UI Text objects have their point size set to zero which returns a very small and incorrect preferred width, this makes it seem like the RectTransform size is not affected by the size of the text.
With regards to UI Text and TMP returning different results / Preferred values when using Auto Size, we can certainly discuss that.
Preferred Width currently represents what the width of the text would be if the width of the text container was infinity and when using Auto Size, this means the width of the text at the maximum of the range. In other words, no restrictions on the text width / the Preferred Width.