This makes sense, but is there any reason MRS would see such a drastically smaller number compared to, what I assume to be, matrix.org instance numbers?
My understanding based on the documentation provided is that MRS seeks federation-enabled, published rooms to index, and is the initiator of the connect. It doesn't expect other servers to reach out to it.
Or would this difference essentially be from servers that decided to disable indexing BUT still federate with matrix.org?
Yes, that's the difference. Loads of Matrix servers have nothing exposed to index, and steer clear of public rooms, and so wouldn't show up on MRS's stats.
Whereas I literally select count(*)'d from the destinations table on matrix.org, filtered on servers which had been federating in the last week(?) in order to get the specific stats above. (And then count(*) of all time for the 150K figure).
This makes sense, but is there any reason MRS would see such a drastically smaller number compared to, what I assume to be, matrix.org instance numbers? My understanding based on the documentation provided is that MRS seeks federation-enabled, published rooms to index, and is the initiator of the connect. It doesn't expect other servers to reach out to it.
Or would this difference essentially be from servers that decided to disable indexing BUT still federate with matrix.org?