When I said Toku's "protective" longbow the drill I is counted already.
This is only an example. The reason I used it is that most people don't go for the drill line if they build longbows. Say for me I will go for combat I/cover and combat I/shock most of the time, with some CG longbows thrown in. This is because the benefit of drill promotions is not obvious until you hit Drill III and IV. People go for Drill IV CKN because they are used as attackers (the collateral keep many of them survived) and by doing so experience comes in quick. By the end of first war I usually have a team of Drill III and IV veteran survivors already. It's rare to use your Drill II longbow to attack (unless I successfully pull out the feudalism slingshot and the longbows will have strength advantage over archers and axes).
In addition CKN has an additional bonus baseline FS even you compare unpromoted CKN to an unpromoted Toku's longbow.
I didn't notice the extra FS given to CKN, I'd always thought their only bonus was collateral Damage, (Only played China once back with Qin was Fin/Ind lol)
I think CKNs are even stronger now in BTS because now they can deal Collateral damage to Siege units because of the new rules about Siege cannot deal collateral damage to other Siege units, but they never said anything about archery units lol!