Maybe.. Is it the final Saga..
Imu said to Super Super Sommers to hurry up there's little time, Luffy stacking up on extra food to not be defeated or at least last longer in gear 5..
Imu's already getting weakened by being distracted, and tanking Thorheim plus the hit right before that.. Even though Imu is huffing and puffing, i will say he's unfazed, so Oda is willingly somewhat weakening Imu on purpose for the narrative.. Or it could be to just make Loki look good i guess..
I believe that final of this arc twicely was foreshadowed in the begining.
Imu will burn the Yggrassil. Look here, giants was feared that Yggrasil will burn, even from the small fire, but Thorheim didn't really damaged it. It seems like there is an ancient legend that told about the End of Elbaf, which will burn in fire. And look on the Mural everything there is on fire. Imu's main weapon is dark fire. So yeah, despite time limit I believe Imu will destroy Elbaf.
As for Imu's future role, you forgot few things:
1. Man with burned face will be connected to Imu;
2. Davy Jones flashback will tell us Imu's story;
3. Laughtale flashback will explore again Imu's backstory;
But why should we care about Imu at that point if Imu will already be defeated?
And that is the answer. Everything we will learn in the future will be Imu-related. Which is why you can understand who will be the FV.