You are trying too hard to make everything MacArthur did an extension of his ego and ignoring some very real, serious, logistical issues with the American military using Aussie troops in the Philippines, starting with the inadequate chemical warfare defenses of Australian troops.The absence of Australian land forces from the Philippines and the final drive on the Japanese home islands, which is attributable primarily to MacArthur’s personal ambitions and vanity, does not diminish Australia’s contribution to Japan’s defeat.
There were a number of instances of Japanese chemical release in WW2 against Anglo-american forces that were not widely reported. Rough off the top of my head list:
Victim, Place/Time, Weapon:
1) Australians, Malaya, 1941 -- Chabin grenades [also known as the Model 1 Frangible Toxic Gas Hand Grenade (SEISAN SHURUDAN)] with blood agent AC [Hydrogen Cynide in acid solution] on a bunker
2) British, Burma near Imphal 1942 -- Queens Own 7th Hussars M3 Stuart tanks received an AC Chabin grenade close assault attacks
3) American, Guadalcanal on 23 and 28 January 1943 -- two or more AC Chabin grenade attacks (See -- Memo, OPD 385 to Gen Marshall, 31 Mar 43, sub: Use of Gas by the Japanese, OPD 385 CWP (3-31-43), NAA)
4) American or Australian, New Guinea, late 1943 - early 1944 -- single 75mm howitzer shell w/blister agent fired at SWPA forces -- captured dud shell contents later tested on Aussie volunteers
5) Americans Manila Feb 1945 -- Multiple attacks with early tear & vomiting gas agents [tear gas (CN), vomiting gas (DC), and Chlorpicrin (PS)] in projected candles on 1st Cav and 41st ID by Japanese Navy ground troops. Additional 1st Cav troopers died from scavenging AC Chabin grenades in Manila shortly later, as reported in a 6th Army weekly report in March 1945. This is the documentation for two of the Manila attacks --
6) Americans, Mindinao, May 1945 -- 24th ID suffers Chabin attack, it is unclear whether this was AC or a non-lethal smoke agent in a Chabin grenade."Memorandum by CPT William J Roberts, CWS, CW Technical Intelligence Officer, Subject: Suspected Use of Gas by the Japanese (HQ, 1st Cav Div, office of the AC of S, G-2, 18 February 1945) provides interviews with witnesses of two accounts where a vomiting agent (possibly Chlorpicrin) was apparently used by an encircled Japanese unit in Manila."
Regards #4 above, some time in 1943 the Japanese fired a mustard gas shell at American or Australian troops in the South West Pacific. It didn't detonate and the contents were tested on Australian soldier-volunteers in May 1944 either directly, or observed, by a US Army 45th CWS Chemical Company observer in Australia.
The following is from a Feb 1946 US Army document summarizing all the chemical intelligence reports received by the Chemical Warfare Service in calendar year 1944:
Some Canadian and Aussie chemical warfare documents, and acedemic papers/books using them as sources, I have reviewed make clear that the standard UK anti-mustard agent chemical warfare suit caused cases of toxic shock in their wearers in a tropical environment after a few hour's use. [See "Keen as mustard: Britain's horrific chemical warfare experiments in Australia" By Bridget Goodwin]"The 75-mm. blister gas shell filled with a mixture of mustard and lewisite,
which was fired from the 75-mn, Type 41 (Regimental) Howitzer,
is described in the pamphlet, "Japanese Chemical Warfare", prepared under the
direction of the Chief Chemical Officer, a, USASOS, MPA. This is the same
shell described in T.D.M.R. 848, pp. 67-68, 3 June 1943.
In Australia physiological tests , including treatment with the usual skin
decontaminants, were carried out under tropical conditions using a sample of
mustard lewisite mixture taken from the captured 75-mm. Japanese shell
mentioned above. Using a 1-mm. drop of the vesicant treated after an interval
of 1 min., the results obtained with British decontaminating ointments
Nos, 2 and 5 were satisfactory, and No. 1 followed by hydrogen peroxide
was nearly as good. Simulated Japanese decontaminating powders (chlomnine
T 19%, sodium chloride 35, and talc 78%; and bleach 10% and talc 90%) were inf-
erior . Hydrogen peroxide alone was quite ineffective (ungraded) (L.H.Q.T.I.S.
No. 2, May 1943, cited in M.I. Directorate, G.H,Q. India, Periodical Technical
Summary No, 21, October 1943).
One of the projectiles used in the Japanese 75-mm. Field Artillery
gun, whose range was 6000 to 7000 yd., was 11.5 in. long, filled with a
50/50 mixture of mustard and lewisite, and weighed 12.6 lb. (ungraded) (Special
Series No, 24, p, 76, 1 September 1944)"
There was a large Anglo-American bio-chemical warfare effort that became effectively a single global one from 1942 on with summer and winter experiments going on across the Anglo-sphere full time with human experiments in the UK, US, India, Canada and Australia.
One aspect of that was a program concentrating on the effects of AC agent Chabin (glass) grenades on various allied armored vehicles from 1942-44.
The fact of the program's existence/scope, how close gas came to being used on Japan, and the reasons why that was so, were a major, for real, post-war conspiracy (along with the full success of Anglo-American signals intelligence) that western academics seems to have sensed in the 1960's, but turned into a Leftist myth over Truman's use of the A-bomb being the first act of the Cold War.
The key findings of the Australian experiments were that mustard gas was 4 times as toxic in tropic climates than Temperate/European (and did far more damage to the gonads of males), that British chemical warfare protective equipment -- particularly their anti-mustard suits -- were toxic to users in tropic climates, and that no one could wear an anti-gas respirator more than two hours in a tropic climate even laying flat on their back doing nothing at night.
This gap in Aussie anti-gas kit was discovered in 1943 and it was an unpublicized logistical reason for MacArthur went "All American" in the drive to the Philippines.
There was a desperate research effort in early-to-mid 1944 to figure out the offensive weapons usage tables given the above that became the basis of post WW2 chemical warfare manuals.
The bottom line of why the Allies didn't use gas in the Pacific was they didn't know how to use the most potent weapons Allies had and could not risk using them until the Allies did (and re-equipped the Aussies with American anti-mustard suits). Once the weaponeers knew the effects, a new doctrine had to be codified and put into a training cycle, then distributed to the troops. This took more months.
It also explains why the US Army chemical Warfare Service had an "All Hands Meeting" concentrating on lethal chemical weapons doctrine, and not flame throwers, that happened at Oro Bay, New Guinea not long after that 75mm shell event and just before the Oct 1944 Leyte Landings.