Personally, I think WB is very useful and needed to break through walls and get your troops into the core faster.
Before the recent updates, using it was already difficult. It dies quite easily. With 4 mortars bombing, spring traps, and other defences shooting at them, a lot of times WBs died before doing any damage to the wall.
With the new update, I noticed the defences now target WB as priority although there are other barbs near them. Also, the WBs now only fancy the first layer wall and refuse to break the inner layers.
I have ever placed a pair of WB trying to break through the 2nd layer but it ran far far away trying to break another first layer wall.
Looks like WB is only good for breaking through first layer. Using it causes more frustration then help.
Perhaps I am not good in using them. Anyone has similar experience?

