Battle Song is an event with a low ceiling, basically the best you can get is 3 extra attack strength.  Looking at this guide about the previous event, that is acceptable for an event, but in this case it’s pretty much its ceiling. The difference here is that when combined with Steward's Worthy it can be quite a bit more. This is a simple event, just use it if you can get 3 attack strength out of it, consider Worthy extra strength valued at 1.5. Sometimes just getting 1 melee strength and 1 Worthy strength is enough value to be worth it.