Youre wrong to think Oda gives a shit about powerscaling.
.
He does, it´s usually related to major plot points. The Giants feared Loki because him being released would be too much for them to deal with it. Xebec didn´t recruit Loki because he was weak, Xebec respected Harald because he was strong, Imu was shocked at Harald being killed because he was so strong, he told the Gorosei to leave Elbaf alone because whoever killed Harald is too strong.
Also he knows who Nika is why would he react to him again.
1. He hasn´t seen Luffy up in person up until this point, but he didn´t have any interest.
2. Oda didn´t have Imu react to Luffy´s awakening in Wano like how he had Imu react to Loki´s killing of Harald.
3. Loki specifically has one of the only 2 fruits that allow you to fight Imu, Luffy doesn´t but tbf, it´ll most likely be added to the list at some point, but the buildup is there...
It´s pretty consistently being portrayed that Loki has a bigger connection to Imu at the moment, though obviously that will change by the end of the manga.