While your assessment of the servers may be correct, I have to disagree on some points.
For one, there is no knowing how much of Lindblum's current population is from the RPC, but judging from my own observations of the forums, my linkshell, and friends of mine, its a significant minority of us that actually have access to open beta right now. Us withdrawing isn't going to bring the population down so significantly when we're only perhaps 40-50 people.
Second, even though other servers may have more overall popularity, Lindblum still gains momentum in the general public over most of the other server choices. This makes it more likely, however small that chance may be, that the server will be more congested for a longer period of time.
Finally, the key difference between those 4 servers and a server such as Besaid is that Besaid is a blank slate with few established communities declaring to roll there. No matter how the populations end up, there's no reason to risk unneeded conflicts of interest by sticking to a server that has already been claimed by these other communities.