Whether we've seen Smoothie fight or not is irrelevant, just like Marines do, pirate crews also have ranks and Smoothie is above Cracker, she is the second Commander while Cracker is the 3rd.
Linlin gave Smoothie a higher rank therefore she is stronger. She also has a higher bounty by about a hundred million, yes, bounties do not equal power, but they are factor we can take in, especially with a character like Smoothie who we have barely seen fighting.