SeaRAM is a rotating missile like a bullet out of rifle. That mean there is added rotational inertia it must overcome if it wants to keep up with a weave-and-bob incoming.
The Sidewinder was originally designed to zoom up the exhaust port of a larger, and less manoeuvrable target going, more or less, in the same direction (that means, the net closing speed is the missile speed itself ~mach 2). Here we are talking about a combine closing speed of Mach 4-5 against a much smaller (and presumably harder jinking) target.
btw, I just wiki 'sidewinder missile', and look at its kill ratio,
"The Sidewinder is the most widely used missile in the West, with more than 110,000 missiles produced for the U.S. and 27 other nations, of which perhaps one percent have been used in combat. It has been built under license by some other nations including Sweden. The AIM-9 is one of the oldest, least expensive, and most successful air-to-air missiles, with an estimated 270 aircraft kills in its history of use. "
That means 1100 missiles fired for 270 kills. A 4:1 kill ratio. That means, of the SeaRAM's 11-shot magazine, it can statistically kill 2-3 attacking fighters from rear end...this looks worse and worse as I type. I think the Navy owes taxpayer a real scenario of shooting 2 inbounding supersonic target drones, and see if 11 missiles can knock down 2.