Let me ask, Can Oden do everything with Ame no habakiri that he can do with Enma?
Remember letting a sword shrivel you up by draining you haki isn’t a skill.
In Actual combat, if Oden uses a one sword style, can he do everything with Ame that he can with Enma? If the answer is yes then why?
it’s because Oden is THAT STRONG. So if Ryuma is even STRONGER than Oden, why would it matter if it’s Enma or Shusui?
We don't know that he can. We don't know that he could not do more with Enma.
Like, if Oden was using one sword style, it's possible that he'd take Enma over Ame no Habakiri.
Enma is the blade that was hyped to possible become of the highest grade, and Enma is the blade that was given to Zoro between the two after all.
The skill is being able to control how much Haki you allow the blade to push out. Without mastery, you're fucked if it always forces all your Haki out.
With skill you can let it draw out 10% more than you normally would be able to without it for more Haki into attacks, or 20%, or 30%, and so on. You can regulate that, and not let Enma's will have the control.
So you can use Enma to gradually increase the strength of your attacks/the amount of Haki you put into the blade to defend, up to the most extreme cases where you really need that much strength into one decisive attack that you're fine with taking the gamble of exhausting yourself.
Again, it's not that much different than G4 in that regard.