But they aren't the same.
Graves is meant to feel like a burst AD caster. It's a part of why the attack speed boost is built into his kit, so that you're not as pressed to build attack speed and can focus on raw damage.
Lucian is much more heavily centered on auto attacking and critting.
They benefit from different things. Thematically crit is not as important for Graves, neither is attack speed. He's not casting that often so trinity isn't really a central item to him, but it can be somewhat useful.
Lucian however deals less damage on skill cast than graves, and his ult deals more damage over time but is much more conditional. Lucians ult is designed to put a lot of damage on approaching targets, graves is designed to decimate an entire team. Lucian needs crit and on hit effects to really shine. Graves is all about raw AD and Armor Pen.
The fact that they seem like the "same" champion isn't due to their design or a need to be redesigned, it's an issue with ADC itemization. Graves has always had this problem (his success is solely dependent on changes to ADC itemizations and less on his actual kit, much like corki), the game does very little to help AD casters stand apart from everyone else who's AD. However there's nothing wrong with the vision for Graves or the vision for Lucian. Most of this will be addressed when we start seeing updated ADC items.
If you really believe at the core, these two champions are the same, or rather were intended to be the same and that it isn't a sign of issues elsewhere, you don't know the champions very well.