Yeah, you could argue, "Prime is sufficiently expensive and video streaming is a sufficiently large part of Prime that it's not dumping".

I can see that, it's possible. I mean, if Prime cost $1, it wouldn't be a good argument, but Prime is more expensive than that in reality. How much of the value of Prime is in streaming video (as opposed to free shipping)? It's hard to say (for an outsider at least, I'm sure someone at the company has run the numbers).

The gray area here does make the situation a little more confusing...

For the sake of argument, what if we suppose Prime costs $1/year and the value of free shipping is more than that. Would that be the kind of situation where the government would take antitrust action?