Very few people understand the nature of the “Three-Fifths Compromise” and point to it as prima fascia evidence of the racism of the Founders. It actually had nothing at all to do with any perceived lesser value of slaves. It was in fact a purely political argument.
The census as required by the new Constitution served two purposes. It provided a count of population for the purpose of apportionment of representatives in the House and also for the purpose of taxation. The Constitution did not allow direct taxation of citizens; all taxes had to be levied in proportion to the population of the states.
Since most slaves lived in the southern states, the slave-owning delegates to the Convention wanted naturally to count the slave population fully, at least for the purpose of apportioning representatives. They wanted to have things both ways and not count slaves at all for the purpose of levying taxes. Lacking slaves, northern delegates naturally argues for the opposite- counting slaves fully for taxation purposes but not at all for the apportioning of representatives.
The compromise was that 60%, or three fifths for any public school graduates reading this, of the slave population would be counted for both purposes. It was strictly a political compromise and did not reflect any idea of anyone thinking of slaves as less than fully human.
Yes, the 3/5ths clause undermined the slaveholding states, which helped blacks. It’d be worse for blacks if the slaveholders had voting power coming from the non-voting blacks counting as whole persons (in counting representatives and electoral votes per state).