Your analysis ignores a few issues:
There's an argument that the bill is unambiguous, and applies subsidies only to those exchanges created by the state. Which would mean that the law is not subject to several interpretations. I'm curious what your argument is that the section on subsidies specifically saying "state exchanges" (where other sections use "exchanges" without the modifier) should not be read as applying subsidies only to the type of exchange listed.
The Court, by longstanding rule, does not treat any words, or omissions, from a piece of legislation as being unimportant or unintentional. An interpretation which says "the legislature made a whoopsy" is not a valid interpretation.
Legislative history and stated purpose of the law are only relevant where the statutory language actually is ambiguous. See #1. And United States v. Missouri Pac. R. Co., 278 U.S. 269 (1929).
Similarly, other sections of a law do not change the meaning of a term in a specific section under review except (a) where the term is explicitly defined elsewhere, or (b) where there is ambiguity. Again, see #1.
And it's the same with Chevron.
Finally, constitutional avoidance (while important) does not mean that the Court strains to find a meaning of the law which cannot be challenged on constitutional grounds. The fact that there is a way to read the bill as not raising any constitutional issues does not mean that (if it is unreasonable) that interpretation wins out. To quote Justice Cardozo: "avoidance of [raising constitutional issues] will not be pressed to the point of disingenuous evasion."
You assume, without proving, that there is no argument that the law unambiguously provides subsidies only to state-run exchanges, and fail completely to address that argument, instead taking as a given that either the law is ambiguous or it unambiguously provides subsidies to all exchanges.
But given that the case hinges on the appellant's argument that the law unambiguously does the opposite, your unproved assumption is fatal to your analysis.