So Imu basically casually repelled all of Gaban's strongest attacks when attempting to know who he is, his ideology and purpose, ended up bleeding in the face because he was focused on killing Luffy underestimating Gaban's all out attack, then finishing him off, slicing his arm apart.
The impressive stuff is that Gaban's attack made him bleed, which also served to give Gaban some hype due to his status as an old legend in decline, but in terms of fighting capabilities, it was a no contest, but then again, by scaling it was obvious