In actual gameplay... it's not so simple.

The rogue's features are meant to allow it to stay mobile and out of danger, and to hide. If you're using Steady Aim to generate Advantage, you're assuming you have no need to move. Which is a GIANT assumption.

Secondly, without Sharpshooter, you're not ignoring Cover. If you're aiming for enemies engaged in melee combat with your allies, so you can get your Sneak Attack off, you may be taking a penalty to hit.

It's just not so easy to peg how the rogue is going to work out generally. If you have stuff to hide behind, you may be ducking in and out of hiding and will have Advantage from being an unseen attacker. But if the terrain doesn't allow for it or enemies are harassing you, then you need to use that bonus action to Disengage, or Dash. Then you might have to target someone next to an ally instead and won't have Advantage. Maybe the terrain favors you and you can Steady Aim all you want, maybe not.

If you do include Sharpshooter, then you really need to be able to Hide or stand still for Steady Aim if you want that bonus damage because you NEED the Advantage. And don't forget that two attacks+GWM means the barbarian not only has the potential to do that damage twice, but also proc a bonus action attack if they kill someone.