For being very slow, you can’t even compare Owl to Alfrike. There’s absolutely no reason at all owl should be very slow.
Compare him to the Guardian Bat, Owl is basically a 5* version of Guardian Bat, yet Guardian bat is average speed. Are people saying Guardian Bat is overpowered? No, of course not.
Last, even on defense, the theory that he will be the last man standing and he will fire, “devastating” the enemy is garbage. In many wars and raids, even average speed heroes in the wing often don’t get to fire. If they do get to fire, the defense has already won the fight anyway. For very slow, they are a complete non-factor in defense (unless in the flank or tank, but Owl wasn’t designed for either one).
Make Guardian Owl average speed.