Egg, you are an excellent educator because you explain the basics, which is where a lot of mistakes are made.

I too create a text Area 99% of the time and also adjust row width to create multiple rows in a mobile variant (although I generally don't use Push). So far we are on the same page.

Now what happens (for me) is I select the text on the Mobile site and Update This Variant, then alter text size from 28 to whatever. The Main site text is now magically 24, not 28. It has to be 28, so I change it back to 28...Mobile site is now 28. Rinse and repeat using different sizes in the Mobile, same result.

Attached example was created thusly:
Create site > add rectangle > add text area > change size and colour > drag text onto rectangle > create mobile variant
On mobile, select text and update this variant > edit size of text > wheels fall off
Confused.web