From: Chicago, Illinois
In my current game, I mostly ignored Luzon and did not land any troops there until early August 1942. It is certainly a viable plan to bypass Luzon and can be very helpful to gain maximum benefit from the amphibious bonus.
There are good reasons to do Luzon first, however. Clark Field remains dangerous and torpedo-equipped Catalinas flying from there can threaten your tanker routes. This forces you to skirt the coast of Thailand with all shipping moving between Hong Kong or the Home Islands and Singapore. Taking the long way burns fuel. B-17 Ds can remain at Clark and threaten ports as varied as Samah, Camh Ran Bay, and Takao. Also, bypassing Luzon means constant vigilance at Cheech Jima and Saipan to guard against re-supply efforts.
There are significant allied assets on Luzon, beyond the Phillipine army: about 100 P-40Es and 25 B-17Ds, for example. If you ignore Luzon, these can be bought out by the allied player and then you will have to deal with them later when they have better pilots.
It seems to me that if you are going to do the Pearl Harbor raid, taking Luzon early makes sense. By the time Luzon has fallen, your CVs have supported the CentPac invasions and are in position to support your move into the DEI. I did not do Pearl Harbor and had KB in position to support the DEI move immediately, so I bypassed Luzon to take the DEI while KB was on-hand.
Good points, but...
1. You have to neutralize the USAAFFE Air Forces regardless of plan. In my bypass plan, you land on Luzon to set-up airfields and start bombing, but other than that you just need to pin everyone in Manila/Clark. You will need to bomb continuously for several months, but eventually after you deal with the P-40Es you can use 2nd rate aircraft and new pilots for training.
2. You can't leave Luzon completely alone, IMO; you have to get into the Manila hex so the Allies stop producing supply there; otherwise that's 100 points a turn and will delay starvation.
I land 2-3 divisions, but then just get set-up in Manila/Clark hexes; by then, early January, you can withdraw the extra divisions for Singapore or elsewhere.
I just don't know why it needs to be taken quickly. Once isolated and bombed, the only practical use to Allies is as a forward refueling stop for subs