We should NOT count any but Citizens and legal residents. Not one Illegal Alien should be included!
The current legal landscape would require a Constitutional amendment to change from the current state of counting everyone, to only counting citizens and legal residents.
But when the Constitution was written the Census directions were set.
We needed an Amendment to end the 3/5th rule and your desire requires an Amendment as well.
You are correct, but good old Article 1 Section 2 calls for a count of "free persons". Not citizens. That opens the census to manipulation by Congress and the Judiciary.