It's only in hindsight that the surface ships involved in the KON Operation can be said to have had little value for the Japanese in the Philippine Sea battle. Before the battle, the Japanese were certainly counting on them to perform significant functions which would enhance Ozawa's offensive and defensive power. The US battleships in the same battle actually were deployed in a way which significantly aided in the defense of Mitscher's carriers. Therefore, the Japanese were completely justified in thinking that their battleships could also be useful to Ozawa; both sides wanted their surface gun platforms available for the battle and the performance of the US battleships validated that strategy.

A heavily reinforced Biak was actually a trap for the Japanese, because MacArthur could simply by-pass Biak by taking Halmahara, which he did in late 1944, and Nimitz taking the Palaus, which Nimitz did in September, 1944. The Japanese simply didn't have the logistical shipping available in the summer of 1944 to keep either the Biak garrison, or an effective air force on that island, supplied. Japanese air power on western New Guinea had been destroyed by General Kenney and the measly few aircraft that remained available to the Japanese to reinforce any Japanese air bases in the entire area could not have made any difference in the timing of the assault on the southern Philippines. The Fifth Air Force would have simply neutralized an Japanese air fields on Biak, as it had done time and time again on New Guinea. The Japanese did contest the island for some period of time, but the Fifth Air Force was using the airfields anyway. In any case, the Japanese IGHQ reasoned, correctly, that holding Biak might delay the invasion of the Philippines, but holding Saipan delayed the commencement of the bombing of the Japanese Home islands, which was far more important to the Japanese military.

Moreover, the Japanese didn't have a regiment to reinforce Biak, they had one badly depleted 2500 man amphibious brigade, which would have faced extremely effective aerial opposition had the IJN tried to put even that unit ashore. The Fifth Air Force had already made a name for itself by ravaging Japanese reinforcement convoys, beginning with the battle of the Bismarck Sea in March, 1943, where the Japanese lost something like 12,000 men and thousands of tons of equipment and supplies, not to mention 16 out of 20 ships, including four fleet destroyers.

The "distraction" you mention would not have had any real effect on the US time table, as the Japanese were overwhelmingly outmatched in 1944 and could not stop one offensive, let alone two simultaneous offensives. It was the Japanese who suffered from the "distraction" of trying to stop the US juggernaut which was bearing down on them.

You claim that a four month delay in taking Biak would have meant that "the Soviets invade Manchuria in 1945 before nuclear weapons are dropped or, that the weapons drops occur earlier into the US bombing campaign." I find that a curious contention because Japanese retention of Biak would have had absolutely no bearing on the timing of either event. The Soviet invasion of Manchuria was dictated solely by the time line of the war in Europe, while the dropping of the atomic bomb, was dependent on the pace of development of the bomb in the US, and the possession of Saipan, which could only have been accelerated by the Japanese attempting to reinforce Biak. The only potential result of the Japanese retaining Biak is a short delay in the invasion of the Philippines, and that is very debatable.