He is as Strong as him Physically, meaning Similar Doriki,
Just like when Crocodile said that Mr. 4 is Stronger than Mr. 3, He was comparing their Doriki, not saying that a Bazooka > Mr. 3's DF,
Just like when Yosaku said that Arlong is much Stronger than Krieg, He was comparing their Physical Power, not their Fighting Styles,
Just like when Brook said that Zoro & Zombie Ryuma are Equals, He was referring to their Doriki, He wasn't saying that his Sword-Style = Zoro's
So Shiryu have same Physical Presence as Magellan & requires same amount of Power for their Health to drop to 0 or Knock-Out,
But Offensively, nothing indicates that Shiryu is as Threatening as an Admiral Level DF
I believe that even if entire Impel Down Cast teamed-up, They would Die against Magellan (Only BB can do something),
Shiryu ain't like that