Tim, I agree with much of what you say, but dont forget that the Japanese attacks finished up on the 19th. The US then spent nearly the whole of the 20th searching for the Mobile Fleet before receiving a report at 1600. Until that point in time I dont believe the Americans really knew the location of the Japanese. So, with all due respect to Rens parameters, the US really could not attempt their interception until that point. Coincidentally, it was not until 1600 that Ozawa was able to regain control of his fleet (after the loss of Taiho he had transferred his flag to a Destroyer, effectively cutting him off from his command. He was unable to effect a transfer to the Zuikaku until 1300). Even so, as you say he was not withdrawing, but he was steaming away from the Americans, with the idea of launching further long range attacks the next morning. He still had, at that stage 130 or so aircraft (many of them unready for action possibly they may have been readied by the next morning)He believed that the Americans had suffered a lot of damage, and that the Guam/Saipan based airpower was still potent. Toyoda gave the order for withdrawal at 2046, I believe this order was given before the full extent of the US air strikes on the Mobile Fleet were known. Toyada was basing his decision primarily on the known losses of the 19th, and the undiminshed intensity of US air activity over the invasion areas.
The question is, therefore, if the US fleet commences its pursuit at 1600 hours insteadf of launching airstrike, can it intersept the IJN by daybreak of the 21st, given that the Japanese were withdrawing at about 15 knots up until 1830, and then increased to 24 knots after that? If the USN does not make the interception by mid morning, there is a strong risk of the US fleet being discovered out of position, being subjected to attacks from undamaged land based air units outside the combat area, and of course the repaired Carrier planes on Ozawas carriers.I doubt that they can, given that the US fleet is going to close at only 3 knots, and still have to find the Japanese. The only way they can even hope to do this is is they detach the fast battleships, supported by some cruisers, and try and run down, corner and sink a part of the Japanese fleet bewfore it knows ehat is happening. Surprising the Japanese at night is no easy task, surprising them in daylight relies on no successful air searches, again an unlikely event.
The best bet was the one the US followed, namely to use their airpower to drive the point home that the US had won the battle, and actually, the war.
I have often daydreamed about what it would take for the Japanese to win the war. They needed time to rebuild their air groups after Midway, and never got that....but what if the Japanese had used their subs to sink merchantmen rathe than on pointless and risky military targets. With an average of only 25% of their subs used on anti-shipping operations, they still managed to sink about 1 million tons of shipping....if they had increased this to say 70%, by simle extrapolation the shipping losses would increase to something like 3-4 million tons. That amount of loss will rule out Guadacanal, and delay the pacific drive for at least a year. The US will be forced to spend more replacing shipping losses, and less on carriers,
Lets assume that the battle still goes ahead in June 1944, but that the japanese have the carriers Ryujo, the uncompleted light carrier conversion Mizuho, and say Shinano. They have two extra fast battleships. They have about 1000 land based air, and a carrier based air component of about 550. Insteadf of aviator with an average of about 150 flying experience, they have an average of about 500-600 hours, slightly less than their US counterparts. The Japanese have sufficient airpower to put 500 aircraft into the Marianas, and a further 500 at Truk, with a further 300 (say) scattered about the Bonins and Philipinnes. The fleet is not out position....it is based at Truk which is still very functional. The excellent Japanese recon forces give proper warning of the invasion fleet, which this time is attacked east of the Marianas, not west of it, by a combined land basede and carrier based force. If I were Ozawa I would put the carrier west of the Marianas, and use the islands to shuttle aircraft to and from the target.....thus minimizing the risk to the Japanese fleet. The US, instead of being attacked piecemeal will be attacked by a stronger more co-rdinated, vastly better trained defending force...things may have been different under those circumstances.....