You've made a very clear case for no US fighters being inducted. No matter what anyone says, a single engined MMRCA is a LCA killer and this fact alone makes it untenable for any government. And trust me, no one in India's power circles sees the F-35 As a "sweetener" at all. Not only is it going to be horrendously expensive to operate, will come almost entirely closed to India (not even "teir 1" partners such as the UK get much access to the actual guts of the machine), is sub optimal for the tasks the IAF wants and would get beaten by the Rafale more often than LM would care to admit, but tell me why the IAF should be the ONLY airforce in the world operating THREE entirely different types of 5th gen/VLO fighter. If you're asking for a nightmare scenario this is it. Low availability, high cost VLO aircraft sat idle in their hangers for a significant period of time requiring intensive maintainence after every flight whilst the enemy with nothing but numbers on its side is at the fence. A mix of high availability 4.5++ and 5th gen VLO are needed along with next gen UCAVs, it makes no sense to put all your eggs in one basket because I assure you this weakness would be discovered at the worst possible time.
As far as the F-18 goes, Boeing are equally desperate to shift the production line to India if India assures them of mammoth sales (>100 units). These days the market for the F-18 has all but dried up and thus Boeing would me more than happy to offload the production to India and continue to earn handsome revenues for this long in the tooth product.