With current U.S Navy power, they can stop us anywhere include SCS, if they decide to stay at Diego Garcia is because there is other big fish to catch...you Indians know better than us. And we like to play Indian's game, you wish U.S in SCS to counter China, we have the same wish that U.S to stay at Indian Ocean that Yankee can turn over the dream of Indian Ocean as it is India's Ocean.
You are partially right about US two prong strategy. Thing is US can't be certain whether India will make alliance with US or considering current Sino-India relationship being strengthened in recent years, due to smart Foreign policy of Chinese, US will try its best to at least make India indifferent regarding China and SCS.
Problem is India's policy is independent and many critics have said that US should rather focus on India now than mending ties with Pakistan. The whole game is not of SCS but China's ambition to connect to warm waters of Arabian through Pakistan to reduce its dependency on IOR and SCS shipping lanes and its access to Gulf and Africa. Its one of the reason US wants permanent base in Afghanistan too.
Due to India's Foreign Policy more focused on its self-interest than being ally of US, India's strong connection with Russia, growing Russia-China and India-China cooperation, things are not in favor of US.
Also, if you look at other smaller countries like Vietnam etc., they know US can't be trusted as an ally whereas they see India as better ally vis-a-vis China. Japan is also trying to get India more involved in SCS and ASEAN nations have already expressed that India should play a major role.
So look at these aims of our countries, India wants to be reckoned as major regional player and eventually a global player whereas China wants to counter-weight US and protect its nearby areas and resources. Only way to achieve this is some sort of Quid Pro Quo between India and China.
Last thing is growing Russian might. If you remember there has been some issue regarding Russian Navy being authoritative near Chinese region and its aim to increase its Pacific hold. Its important for China to make few compromise too regarding Russia.
There are many more things that I can comment on. My point is that China's interest in Maldives, Myanmar etc. is not just because of India, which it thinks it can make friend with, especially because it is not good to keep a hostile country of size like India if you are facing superpower like US.
Chinese know that they can handle India anytime and India knows this. That's why India hasn't taken any side yet. It is letting US to face China while maintaining good relations with both, with more stress to normalize relations with China, given such a long boundary we share.
You are right about US Navy might, but they know China can become formidable Navy w.r.t them within a decade.
Hope I cleared few things to you.