LOL
The only things they have in common is being two badass swordmen. Other than this they are two very different characters who are only apparently similar.
If we analyse them, for some things, they are polar opposites.
Here some examples:
- Zoro fights because he has a clear goal in Life, Guts instead doesn’t even know if he has one and fights anyway, while wondering what makes him keep going.
- Zoro is completely at ease with his beastly nature, but for Guts is a self-destructive impulse that gives him strenght but needs to be constantly kept in Check.
And there are many others...
Basically Guts is a relatable and deeply human character while Zoro is a narrative archetipe.
And they both work perfectly the way they are.