nah
Loki will never be more relevant than he is now in Elbaf.
Imu isn’t even physically on the island. We don’t even know his backstory, his powers, or even what he looks like.
Imu doesn't need to be physically on the island, his power is about possessing and controlling people from the shadows, which he might not even really be able to leave his throne or whatever.
But the flashback was about:
How Imu killed Rocks(essentially)
How Imu killed Harald(essentially).
His backstory isn't given, but plenty of OP villains didn't get a backstory in their introduction arc anyway, though we saw stuff about the mural and Nika, which is all obviously related to Imcel, as well as the fact that he hates Davy Jones. He's certainly the focus of the arc. As for Loki, as long as he's tied to Imcel, he will remain important. Loki is even likely going to be relevant with Blackbeard as a FV as well, because of Xebec.
While Loki was always strong, being a high top tier since 14 years ago, the human characters are rapidly growing in strength at a rate Loki just isn’t.
This isn't even true. Loki's growth rate allowed him to reach top tier level as a 16 year old in giant years, eventually shocking Imu and amazing Gaban at the same age. What do Kidd, Law and Sanji have to compete lol?
Loki is strong and important. But he’s not the end all be all. If Oda can introduce top tiers like him and Shamrock out of nowhere, you really think we won’t get massive boosts to legacy characters or new characters that even outshine Loki?
Nah,why would I randomly assume that lol? Loki has one of the fruits needed to fight Imu, is connected to Luffy borderline chicken wings tier through the OG Nika this chap, will of Xebec and Harald.....
If Burn Scar man and some Lunarian prove themselves stronger, we can talk about it then, but there's no reason I would grant that currently.