ok. home now.
Manila's actual defenses are:
26 x 75mm
8 x 3in DP/AA
3 x 40mm
3 x .05
(+ ship AA)
That makes 34 heavy AA guns or about 3 batteries worth. (in my interpretation and in the mod, a decent defensive shield)
Your tests showed between a 5.1 -6.3% loss rate. With the heavies silent - 1.4 - 2.6%
Since LBs can be easily set to 20000 whereas DBs will always drop down (and TBs sometimes) removing the AA gap really hurts the DBs and the TBs much more than the LBs.
Yes, it will hurt the DB's and TB's more, particularily the unarmored Japanese types. This is an acknowledged con in order to promote a better overall LB experience (without having to institute a house rule prohibiting bombing at low level) However as stated, I dont consider these losses 'overly' excessive given the number of weapons present, esp when factoring in that some of these "flak" losses as listed by the game can be considered write offs or ditchings while returning to base. US planes tend to be tougher and face less capable flak models.
Ironically, a test I ran gave me higher losses (27 tacticals)
However to balance this; I achieved the following:
Allied Ships
SS S-40, Bomb hits 3, Torpedo hits 1, on fire, heavy damage
AVD Childs, Bomb hits 1, on fire
SS Shark, Bomb hits 2, on fire
AS Holland, Bomb hits 1, Torpedo hits 1, on fire, heavy damage
PG Isabel, Torpedo hits 1, on fire, heavy damage
SS Stingray, Bomb hits 2, Torpedo hits 1, on fire, heavy damage
SS Spearfish, Torpedo hits 1, on fire, heavy damage
SS Sculpin, Torpedo hits 1, on fire, heavy damage
SS Seal, Torpedo hits 2, on fire, heavy damage
DD Pope, Bomb hits 3, Torpedo hits 3, on fire, heavy damage
SS Snapper, Bomb hits 3, Torpedo hits 2, on fire, heavy damage
SS Skipjack, Bomb hits 4, on fire, heavy damage
SS Porpoise, Bomb hits 4, on fire, heavy damage
SS Seadragon, Bomb hits 2, Torpedo hits 1, on fire, heavy damage
SS Perch, Bomb hits 1, on fire
SS Sealion, Bomb hits 5, on fire, heavy damage
SS Sturgeon, Bomb hits 1, on fire
SS Permit, Bomb hits 2, on fire
AK Paz, Bomb hits 1, on fire
PT PT-41, Bomb hits 1, on fire, heavy damage
DD Peary, Bomb hits 3, Torpedo hits 1, on fire, heavy damage
SS S-41, Bomb hits 3, on fire, heavy damage
AV Langley, Bomb hits 7, Torpedo hits 1, on fire, heavy damage
SS Tarpon, Bomb hits 1, on fire
SS Sailfish, Bomb hits 4, on fire, heavy damage
SS Searaven, Bomb hits 2, on fire
DD John D. Ford, Bomb hits 1, on fire, heavy damage
SS S-38, Bomb hits 3, on fire, heavy damage
PG Tulsa, Bomb hits 2, on fire, heavy damage
AS Canopus, Bomb hits 3, on fire, heavy damage
SS S-37, Bomb hits 1, on fire, heavy damage
AK Ethel Edwards, Bomb hits 1, on fire
SS Seawolf, Bomb hits 1, on fire, heavy damage
SS Pike, Bomb hits 2, on fire, heavy damage
AK Anakan, Bomb hits 1, on fire, heavy damage
AK Corregidor, Bomb hits 1, on fire
MSW Finch, Bomb hits 1, on fire, heavy damage
MSW Bittern, Bomb hits 2, on fire, heavy damage
AK Bisayas, Bomb hits 1, on fire
SS Pickerel, Bomb hits 2, Torpedo hits 1, on fire, heavy damage
AK Princess of Negros, Bomb hits 1, on fire
SS Sargo, Bomb hits 3, on fire, heavy damage
AK Compagnia Filipinas, Bomb hits 2, on fire, heavy damage
PT PT-32, Torpedo hits 1, on fire, heavy damage
SS Swordfish, Torpedo hits 1, on fire
AO Pecos, Bomb hits 2, on fire
SS Salmon, Bomb hits 1, on fire
AK Palawan, Bomb hits 1, on fire
PT PT-35, Bomb hits 2, on fire, heavy damage
DD Pillsbury, Bomb hits 1, on fire, heavy damage
MSW Tanager, Bomb hits 1, on fire, heavy damage
(lol....i can sort of see now why some players choose to bomb Manilla instead of PH)
One other consideration though i admit i'm "reaching" a little here [;)] I consider an attack like this to be actually two attacks in one. Remember WitP's abstractions despite the illusion of specifics here. Six carriers of the KB were not capable of launching such a large mass attack at one time. In reality it would be two waves (as was the orig PH attack)
Under such an interpretation, thats about 13 planes lost or written off per attack against an alerted defense. Again, not bad given the level of damage caused.
House rule:
I'm not saying your 'house rule' isn't a viable solution but i still feel that such a rule is too restrictive because despite the impressive power of the heavy flak guns, there remain many situations (and bases) where low level bombing can be a profitable and valid tactic (one example would be the bombing of LCU's outside of a base) I also feel that players should be willing to make the choice to bomb at low altitude. Only difference is now they have to be willing to pay a heavy price in morale, damage and of course lost planes
The damages on the tacticals dont overly concern me because in general repair rates for aircraft in the game tend to be rapid....more so with the CV's. An oft voiced player complaint has been that CV's can ahistorically camp off a base and pound it for days. This was the main incentive for the aircraft ordinance point rule being added. In combination with a heavy degree of damage to repair (against a well defended base) this will be a less frequent occurance.
A better solution may be for me to partially disable some of Manilla's defenses to allow a suprise attack option on this city as well as Manila for those who prefer to bomb Manila instead of PH. (Personally i always start with the PH attack)