The fact that Pica has a sword does not automatically make him a swordsman..
If i remember correctly Senior Pink had a sword, but he is a brawler. Baby 5 has all kinds of cold weapons and firearms, but it does not make her into a master of this disciples. Diamond, is another example, caries a sword with him, but does not know how to use it properly. Dofla and Gladius caries guns… and so on
So the fact that Pica has a sword does not make him into (experienced) swordsman. Therefore, there is nothing anticlimactic or random about this scene…
Oh but it does. If you possess any degree of skill in the art of swordplay then you are, by definition, a swords(wo)man. If Pica didn't have faith in his skills as a swordsman he wouldn't use one to take a swing at a 400 million bounty pirate that he swore to not let anywhere near his boss.