It is a legit opinion anyways. My point follows the logic of Zoro being capable to defeat stronger foes than before because sword duels tend to rely on a small number of powerful slashes that hit the target, and with Enma he's able to go up to a "risky level" that allows him to defeat stronger people faster in a "investment of haki" but also weakens him much quicker against enemies that are much above.
Anyways, I get your point and is a valid one.
Thing is, I'm not sure that would be the case.
Lets say Zoro wants to do a 5/100 attack.
Enma steals haki and makes it a 15/100. Result = You wasted haki.
Let's say Zoro wants to make a 100/100 attack.
Could Enma make it a 105/100 or a 110/100 attack? Considering that what Enma does is using the
wielder haki power I don't even know if it is possible to go beyond the natural limit of 100/100.
So if that's the case the only "benefit" ( = drawback) is that you overkill fodders.
So "magic sword" my ass. There's a reason Kinemon & Co. didn't even want to touch it.
[Just for context: I think that Shusui was a PU because while Zoro couldn't immediately extract the full potential it certainly did not make him weaker, and clearly gave him and immediate boost w/o significant drawbacks]
Anyway, Zoro has already partially mastered it probably, so he's already stronger. How people want to define the process is up to them.