Let's go back to the part where you said slavery wasn't in the Constitution.... why were you wrong about something so simple and basic?
It’s not. Slavery in no way is outlined, ratified, explained, given right to, etc. It existed before the constitution. The three fifths was a compromise between non-slave state’s and slave states. Non-slaves states didn’t want three fifths, they wanted slaves to not count at all. Zero. Slave states wanted slaves to count as full citizens. They compromised at three fifths.