No offense, but did you read the article?
You should at least read the section “Wouldn’t UTF-32 be easier for everything?” and the following two sections for the context here.
So, everything you’ve said is correct, but it’s irrelevant for the grapheme count.
And you should pretty much never need to know the number of codepoints.
yup, my bad. Frankly I thought grapheme meant something else, rather stupid of me. I think I understand the issue now and agree with you.