Is the Xbox series x controller worth it if I already have an Xbox one controller?
Not really, after all, the Series X controller isn't that much different (which is good too)
It would make perfect sense from the following points:
USB type C connector
Share button
Improved feel
Improved processing
Renewed keys (RB, LB, RT, LT)
Novel D-Pad
Bluetooth 5.1 + standard Xbox wireless connection
That speaks against it:
Not every battery pack (not the battery itself, but the capsule) fits into the new controller