The core issue is that a transformed Loki completely dominated an
amped Harald. This is a character who, by narrative implication, stands above the likes of Xebec, Prime Whitebeard, and Roger.
I can genuinely say with confidence that Loki has already surpassed both Xebec and Harald. That’s what the narrative keeps pushing. Loki, even before eating the fruit, was able to get past Ragnir, someone Harald was only confident in challenging after receiving his amp. That already establishes Loki as relative to base Harald before gaining the world-destroying fruit. There’s also a panel of Loki clashing evenly with Harald, so there’s nothing in the story that contradicts this interpretation. If Shanks ends up beating Loki outright, then powerscaling genuinely falls apart.
Even Gaban wasn’t confident that Luffy could handle Loki, despite knowing that the same Luffy had already beaten Kaido. On top of that, Loki has been explicitly established as nerfed for months. We might not even see Loki’s full potential until post-Elbaf.