Guess what...
Oden is the only one who "tamed" Enma
Oden is the only one who gave "scar" to Kaido with "Enma" and yet he is not the one who defeated Kaido
Luffy is the only one who beat Katakuri
Zoro is the only one who is wielding Wado Ichimonji...that made his life bit easier
the key here is "only one"...
and again it has nothing to do with the power level...it is dependent on users "energy"....Zoro has large amount of "ryou/energy" than normal person....
again this is same as Luffy absorbing 100 shadows in thriller bark....only difference is that is temporary and this is "permanent" power up....
And Scabbards strength varies from Kinemon to Ashura (like from veteran to YC3 at max) ....
bottom line is ......"you need to have sufficient amount of Ryou"...