I think the biggest problem of OP post TS is Oda failiure to convince us to like side characters.
Pre TS had Wiper,
CP0 agents(before they were revealed were too iconic),
Alabasta King was better than Dresrossa,Impel down and
even in mid arc like amazon lily.
POST TS:Rebecca
Uselss people in Dresrossa
Scabbards
FI people
Only one I liked is Cavendish and Barto from 100 usless ones