The second person singular (thou/thee) is now outdated in English but still very common in other languages.
Third person singular distinguishes between masculine, feminine & neutral, whereas the plural does not.
"We" is ambiguous - it includes "I", but does it include or exclude "You"?
"It" & "You" manage perfectly without specific object forms.
French & German complicate things even more.
I think a super-simple language can get by with only four pronouns, for example:
|I - Me|
|Thou - Thee - You|
|He - Him - She - Her - It - They - Them|
|We - Us|
Genetives, datives, reflexives etc can be handled by affixes, to be dealt with separately.