It wasn't the lack of armor or even a few Spitfires that doomed Malaya and Singapore. The Commonwealth forces were outfought, partly due to inadequate training (especially evident in the Indian Army units), poor leadership on the part of the Commonwealth (starting with the top and working down to the battalion levels), but mainly due to the superior tactics of the Japanese. Yamashita used the elite, often combat veteran forces under his command brilliantly, including the use of amphibious jumps to outflank defensive strongpoints, to maintain unrelenting pressure on inexperienced colonial forces.
Even if the proposal that the lack of equipment was the key to defeat, the question then becomes where that equipment was most needed for the British war effort. Clearly defending the British Isles had to be priority # 1, maintaining control of Suez was more important to the fight against the main enemy, Hitler's Reich, than providing additional assets to a position that was already considered to be impregnable. The British of late 1941 were not the U.S. of late 1945, with so many aircraft and ships coming off the assembly lines that storage of them was a significant issue, they were a largely blockaded country fighting a Continental power that outgunned them and had equal production capability.
Even if the proposal that the lack of equipment was the key to defeat, the question then becomes where that equipment was most needed for the British war effort. Clearly defending the British Isles had to be priority # 1, maintaining control of Suez was more important to the fight against the main enemy, Hitler's Reich, than providing additional assets to a position that was already considered to be impregnable. The British of late 1941 were not the U.S. of late 1945, with so many aircraft and ships coming off the assembly lines that storage of them was a significant issue, they were a largely blockaded country fighting a Continental power that outgunned them and had equal production capability.