I'm assuming you're referring to the fact that you have to hit Ending before applying Closed Position on someone else?

While I do agree it is kind of clunky, undoubtedly the skill is designed like this to prevent enterprising Dancers from just repeatedly swapping Closed Position on different party members until both DPS are buffed with Standard Finish. While this is feasibly hard to pull off, it is still possible seeing as Standard Finish lasts a minute and Standard Step only has a 30 second recast. Once both DPS were buffed all the Dancer would have to do is recast Standard Finish every 30 seconds to keep both DPS buffed, which goes against the Dancer's unique partner system. This is arguably why Technical Finish exists, is to give Dancers the opportunity to provide for the rest of the party outside their Dance Partner.

Your comparison with Kardia is flawed seeing as Kardia only provides healing and not a long-lasting 5% damage increase, and as a healer being able to swap Kardia to whoever is taking more damage at the moment is important.