Brave Lucina vs. Shiro

He is different than her. Not essentially better or worse, they just don't fit the same role.

Shiro is a pure ennemy phase tank.

B!Lucina is a mix of offensive and defensives as well as a very good support for physical fast teams.

So really they aren't the same, just see what you need based on your team needs.

To replace Brave Lucina? Hell no! But if he’s a unit you like and want to add to your army go for it.