Because Rocks had a full fight; for Harald we had very little in comparison. Also, oda already showed his haki against Xebec.
He decided to show it only with Loki because end of the day he was the focus.
For harald fight we had fair a amount just most of the time he was fighting fodder .
It was more than Roger and garp VS DR rocks to tell the truth lol.
The main fight for harald was 1 page lol which was vs loki and harald came back to sense and let loki kill him him .
Which is why can't compare the fight because DR Rocks did not allow Garp and Roger to get free attack on him .
They also knock him out of DR and he went back normal while that could not happen with harald .
Story wise the way how fight were showed were very differnt on how they were done and meaning in story also.
That why i don't say you can't compare and use the fight sin term of power scaling .