This is so profoundly ignorant that I am surprised it continues to come up.
Under your premise you would have wanted all Slaves to be counted as whole persons. This is exactly what many slave owners wanted, they wanted to have the slaves counted as whole persons so their states would have more power.
The Abolitionists wanted the slaves not to be counted at all
3/5ths was a compromise and directly lead to the eventual abolishment of slavery completely.
Under your premise you would have wanted all Slaves to be counted as whole persons. This is exactly what many slave owners wanted, they wanted to have the slaves counted as whole persons so their states would have more power.
The Abolitionists wanted the slaves not to be counted at all
3/5ths was a compromise and directly lead to the eventual abolishment of slavery completely.