They had much potential but both storywise and combat-wise they never came close to reaching it with Oda bothering far less with writing and developping them that he did with Baroque Works, the Donquixote Family and Big Mom Pirates; he was too busy overhyping Oden and having other characters worship and sing the praises of him; while the plot was ridiculously against them as were nerfed, dumbed down and had everyone fighting or sabotaging them.
Plus the history, relations and dynamics of the crew were cruelly neglected and underexplored with even the interactions between Kaido and the Calamities being severely rare and underdevelloped, we didn't even had any real interaction between Kaido and Queen.