You would need to ask oda that. Only DR xebec showed continuous haki barrier. Imu has always used omen maki to block loki's attacks. When he was hit directly , he was sent flying and was huffing and puffing.
Neither imu nor Hk amped xebec showed a haki barrier like DR xebec did for whatever reason but it doesn't change imu's haki is vastly superior lol.