It's certainly a credible thesis that's being offering here, and yours is probably the best formulation I've heard of it.
Still, from my own brushings with folks in "professional circles" -- they tend to be pretty consistent about packaging assessments such as these with probabilistic labels (e.g. "likely", "highly likely" and so on). My main concern here is quick toggling to "known" or "near certain" status (or insinuations that "everyone in the IC believes this", which I am noting is not your intention here, but it did sound like it at first).
It's also just a general policy I like to follow with events out in the real, messy world. No matter good our "model" may sound (to our own ears) about what someone did or why, it's always entirely possible we're missing something basic -- not so much a piece of bombshell evidence, but about the broader human context; or that our analysis is simply flawed.
On top of that there's a significant tail risk that comes with putting too much stake in our models, especially when they get coupled together, and motivated reasoning inevitably starts to kick in.
On a finer-grained note (and to explain why I can't assign this narrative too high of a degree of likelihood): It's not automatically clear that the Russians could have traded Snowden in by now -- they may be asking too high of a price (since he's apparently way more valuable than anyone the US has in their trading deck), and since 2014 they may have been coupling it with their hopes that the US will decide to start being "reasonable" about the situation in Ukraine (and so his transfer would be coupled with a deal in regard to that situation), and so forth.
I also don't see how we know that "they already had all the files he had leaked", or that anything about his case has the potential to destroy the intelligence relationship (which has always found a way of surviving, despite all the bile and vitriol we see on the surface).
(This is all in regard to the "weak" version of this model, that Snowden acted independently but had to have broken once he got stuck in the Motherland and was forced to ask for asylum. The "strong" version in the sibling post -- which asserts that he must have been cooperating with his current hosts from the very start -- has just way too many plotholes, and is way too top-heavy in my view. Not to be dismissive, but I have to limit my time here, so that's all I can offer on it at the moment).