Oh, I'm not saying I proposed the perfect attack force. Certainly if you ONLY care about the BBs and not the subs, an ALL airforce attack force would be best. I just took the OP's germany attack force and modulated it as he suggested - first removing the DDs (which as I expected gave him a slight improvement) and then replacing them with additional subs as he described.
when you say '5 bom, 1 CA, 4 sub, 0 DD against 4 BB and 4 sub is less then 7%.' I'm not sure what you're saying or where you get that from. The sim I used said it would be about 9% to clear the zone completely and only about 4% possiblity that any of the BB's survive. Maybe I'm doing something wrong, or the Sim I'm using is buggy with its order of loss.
Any hits from the fodder boats (CA, 4 Sub) would be taken first against the subs, but once those fodder boats are gone, or the subs are gone, it's bombers against BBs. and most times it seems the Bombers should win out.
Now that I think about it, the one thing that may not be factored into the sim is that it would make sense for the defender to take any
boat hit against the defending subs. The sim probably automatically assigns the first 4 hits to damage the BBs even if they come from other boats, which would be sub-optimal, given the bombers can ONLY hit the BBs, so you want to direct any non-Bomber hits to the subs. I guess it would take a pretty clever sim to really get good numbers on this.