I agree with that reading, but at the time, but for their skin color, slaves would have been citizens. It's understandable their inclusion was intended as a result of the 14A. But counting bodies without consideration of their legal status can't be in the spirit of what intended in the 14A. There is no rationale for giving illegals representation in the government of this country. I hope Trump's administration finds a way to get this to the SC for a definitive determination.
I don’t know how free blacks were counted, but I’ll assume they were. As for getting SCOTUS to rule than not counting non-citizens is Constitutional, I really doubt they’d do that. It would be overturning 250 years of how the census is conducted.
And then there’s the practical aspect. As it is, just getting a reasonable accurate count of people is apparently next to impossible. Imagine if the census workers were required to establish the citizenship of each person in the tally.
Easier by far to deport the people who are not here legally.