Kinshi IS Elemental Attack + BG Increase!
Herc can have 15BG per attack during her buffs, while Shingen will sit at 14.5 thanks to her passive effect. For everyone else, if you have a lot of buffs for combo attacks, then you cut down on 1 attack overall. In some cases that is enough to Burst a turn earlier. It kinda depends if you can make use of the extra 2BG per attack or not.