Apples and Oranges in terms of physics.
The Loki attack was more of a push. Luffy got caught by the momentum mid swing.
It's similar to the meme videos of kids getting caught by those rotating playground bars.
If Loki would hit Luffy mid air the conventional way, he would send him flying to the next island.
Kaido hammered his Kanabo into Luffy's brain.
If you don't see the difference here I don't even know where to start tbh.
At the end of the day Imu either needed to use the biggest makiblast we have seen till now or gigantification of himself to block/clash with Loki's swings. That tells you the whole story.
And the "bigger one" move was a lightning beam. It's =/= to lightning powered Ragnir swings.
That wasn't a push. Luffy explicitly asked Loki to give it everything he had physically so he could use the impact to gain momentum, just like he asked Sanji, Bonney, and Franky to give it everything they had in Egghead.
Lightning doesn't propel Luffy. In fact, it doesn't even move him from his position. You can look at EVERY example of Luffy getting hit by lightning, especially the last time Loki hit him with it.
Loki was expecting to physically hit Imu, just like in his previous attempts:
This time, he increased the size of his
lightning. . Notice that his
lightning is covered in lightning, but only to a small extent. Even if he failed to hit Imu with the hammer itself, the larger lightning discharge could still hit him. That doesn't mean he wasn't trying to hit Imu with the hammer. That's why Luffy stepped in front of him and asked him to use everything he had and not hold back.
Loki's physical attacks have been reduced to this:
Kaido hammered his Kanabo into Luffy's brain.
Exactly. Kaido broke through Gear 5's defense and drove his kanabo straight into Luffy's brain.
And here, Luffy literally asked Loki to hit him with everything he had, and it did absolutely nothing to him.