How many series have the Indians won with Agarkar? In the recent past (last 4 years), just 4, including 2 scratchy wins against Zims. With Williams and Bracken, the Australians actually won an ODI series in India, but they still don't last long. Williams has a bowling average of 22, all against good teams. He also has 2 five-wicket hauls having played a lot less. Bracken can get under the skin of many an Indian batsman. Never has any Indian fast bowler got figures as good as them.
Depth is not lacking, but quality is. Agarkar is only the best of a bad bunch, so if he's missing, the team misses nothing. They won that last series without him. He's very much the Indian Flintoff, but not as powerfully built and nowhere as effective, but has been a failure for the last 4 years. If there was a McGrath or Pollock in the ranks, the team would win more series.
Bracken is not world class in a team of bowling legends, but can walk into any Indian pace atack of today.
They don't need someone who's established but does not perform. They need a legend. If Agarkar is a good bowler, so are the reserves and other pace bowlers in Indian domestic matches. Legends don't perform in just 1 match- they perform consistently. Yet the Waugh brothers are not indispensable.