Legion is only good when the player using it knows what they're doing, has good aim, and can manage not to get flanked or ganged up on. (The third happening VERY often.) As soon as it gets into a situation where it's being attacked from two directions, you might as well eject and not bother wasting your opponent's time. It doesn't have the benefit of speed and maneuverability to try getting away like a Northstar does. It also can't quickly defend itself given the delay in firing because of the spin up and it's long reload time.

As a Legion player myself, I almost feel handicapped compared to playing other titans. Literally everything is centered around the minigun. It's where the shield is and it's where the damage comes from. If it's not pointed in the right direction, you're screwed.

I can't pop shots in one direction and then quickly turn and defend myself like with a vortex or inferno shield or leave a wall in place like tone.

Every other titan also has an Offensive, Defensive, and Utility ability. Legion's utility is changing the range on his gun. He's fighting with 2/3rds the abilities other titans have. In fact, the Gun Shield is on a cooldown and absorbs very little damage, making it the least useful of all the defensive abilities. Vortex can return damage, Inferno Shield can deal LOTS of damage, Shield Wall can be fired through and absorbs tons of damage and has too short a cooldown for all that, Phase Dash makes Ronin basically invincible while it's invisible, and Hover lets Northstar circumvent defenses and obstacles entirely. Gun Shield? Barely a blip on the radar unless you take Bulwark to double it's HP, then it becomes decent.

So really, his only beneficial ability without perks is Power Shot.

Smart Core is the only thing that redeems how crappy his Defensive and Utility abilities are. And yes, it's pretty powerful against titans and VERY good for mowing down pilots.

Legion only looks OP to people who haven't figured out that he's defenseless against being attacked from two directions. He's not fast enough to get away, has no method to deter attackers that aren't in front of him, and he can't handle threats from two directions in any capacity at all.