Well it may be easier to modify the mtext to make the sheet number reliable.
Your choices are as you listed in you first post as well as plain text.
The problem with mtext as you have discovered is the use of formatting characters.
What ever you choose is up to you & how your drafters will adapt to the change.
As for the amount of code, that is a small price to pay for getting the job done
in a timely manner. SO I don't see the volume of code being the criterion for
consideration of which method to use. I would be more concerned with the impact
on the staff & production both short & long term.
My 2 cents.