US definitely wants India to be propped up against China. But they must have also seen India's performance firstly against Pakistan last year and now China.
Deja vu for them - heavily arming South Vietnam against North Vietnam at the tail end. South Vietnam forces crumbled like a pack of cards once US withdrew. Indian scenario would not be as bad but still.
They also need to take into account whatever India may tell them, it has little desire to military engage China. So US would be mindful.
We then come to the fact that US premier technology will be interacting with Russian tech. Will they allow it?
For India to opt for F35, are they going to let go to a very strong Russian relationship built upon 70 years. Russia will not take kindly to that. What will be their response?
It will also give China ample data about US systems. Which is the last thing US wants right now.
HYPOTHETICAL SITUATIONIndia is ready to abandon the Su-57 and focus on buying the American F-35s
Lets say India buys F35, will it be easier for China to extract intel, from India or other F35 users?
Note: Anyone can answer this, not just the people I quoted.