When Warnock paid £11 million for Josh Murphy, he was 23 years-old and had just fully established himself in a Norwich team that finished 14th in the Championship.
After three seasons at City he had a season-long loan spell with Preston, which was a complete failure (0 starts and 0 goals, just 12 sub appearances). He then had to drop into League One for two seasons with Oxford before moving back to the Championship with Portsmouth.
Murphy started 22 games for City in the Premier League, made 7 sub appearances and scored 3 goals. He wasn't a disaster in the top flight, but wasn't a success either.
Most of the evidence suggests the middle of the Championship is his level.