The AC Tifa PAK is amazing but her joint exposure sometimes makes me go, "... It wasn't Cloud who was the puppet...
It was you..."
The ball joints and their exposure is the cost of greater articulation. The biggest criticism the original Play Arts had were their low detail sculpts, limited articulation points, and overall lack of detail. PAK were a response to that criticism and each PAK is made to be able to properly recreate several memorable or dynamic poses.
Bring Arts are a response to the PAK's criticisms of being too big, too expensive and too doll jointed. They're sorta like Square's equivalent to figmas which are small but high quality figures that include numerous elements and varying hands/faces/etc to create unique poses and expressions. They're cheaper, less scarce, and don't have as many articulation points, meaning less ball joints.