No one but Luffy in the alliance could probably challenge an Admiral in a solo fight. GB lolstomping the alliance without Luffy is a real possibility.
		
		
	And Luffy isnt challenging GB, Luffy is beating GB if they fight. Itll be a high/very high diff fight though.
 
				 
 
		 
 
		 
 
		 
 
		 
		 
 
		 
		 
 
		 
 
		
 
 
		 
		
 
 
		 
 
		 
 
		