Why a better defense of Manila Bay could prolong the Philippines campaign

Could MacArthur have defended the Philippines if he had taken the Japanese threat seriously and prepared properly?

In the proposed counterfactual, he could hold Manila Bay and preserve a landing point for reinforcement or return, although Japanese strength would make it difficult.

In this counterfactual, better preparation would allow MacArthur to hold Manila Bay. Keeping that position would prevent the Philippines from falling completely. A defended bay would also offer a place to land supplies or a returning force for a later campaign. Japanese firepower would still make the defense an uphill battle.