Staging through China from India was obviously dumb. Not sure Darwin would have been any better, and in no case would it hit the Japanese home islands. There's a reason why thousands of Marines and soldiers fought and died over the Marianas. It wasn't the moonlit walks on the beach.
But remember, when B-29 operations against Japan from China were first discussed in January 1943 at the Casablanca Conference, the B-29 had only flown 4 months previously and US was fighting in the Solomons and New Guinea. Deployment to India was delayed by the problems with the B-29. It was only after the "Battle of Kansas" in early 1944 that they were able to deploy to India via Africa in April. And it was scaled back from 2 Bomb Wings to 1 due to progress in the Central Pacific.
And the Japanese didn't just sit idly by. Operation Ichi-Go from April 1944 pushed deeper into China and allowed IJA bombers to threaten the B-29 forward bases. So for two months between late Aug and late Oct 1944 the XX Bomber Command were not flying missions against Japan.
The island hopping campaign in the central Pacific wasn't approved until the Quadrant Conference in Aug 1943. Planning for the first step, Operation Galvanic to the Gilbert Islands, didn't start until the beginning of Oct and the first islands targeted were invaded in Nov 1943. Those relied on the many ships that were only coming into service during 1943.
The air bases acquired and / or built on the islands taken in these early campaigns provided staging posts for later B-29 deployments to the Marianas (places like Kwajalein taken in Jan/Feb 1944). The Marianas campaign for Saipan, Guam and Tinian took place June - Aug 1944. Then the massive air bases and supporting facilities needed to be built. The first B-29 didn't deploy to Saipan until 12 Oct 1944. It was 17 Nov before the first mission was flown to Japan.
So in January 1943, the only possible route to deploying the B-29 against the Japanese Homeland, dumb though it may seem in retrospect, was from China.
Edit:- The XXI Bomber Command came into existence on 1 March 1944. It was to be responsible for B-29 operations from the Marianas.
The second B-29 Bomb Wing to be formed, the 73rd, was then training in the USA. Originally to go to China under the, XX Bomber Command, in June 1944 it was transferred to the command of XXI Bomber Command and prepared to move to the Marianas.
Meanwhile the 58th BW operated in the CBI until it flew its final operation there at the end of March 1945. It then moved to the Marianas to join XXI BC. It then moved to Tinian in April flying its first mission from there on 5th May.