To be clear, anybody with enough compute spend to DDOS #X can bring down every #Nostr relay for a lot less money.
Discussion
Noted.
But you have to know which ones to get.
Are you under the impression that creating a list of the most popular relays would be a difficult task to accomplish?
I don't think that we are a very valuable target. Most of us use at least 4 different means of communication.
Most of us are glad NOSTR even works.
If it goes down it will be in a situation that won't matter.
Tor gets attacked all the time and it still is a spooks best friend.
We are small peanuts.
My relay will just change tor addresses.
The problem is finding all the relays & the subsequent ones that pop up.
This is why it's important for us to run our own private relays on top of supporting good public ones.
As it stands today, that is a trivial task.
Not to say #Nostr won't grow into a landscape where relays thwart attacks or dynamically respawn to dodge them, or some clever adaptation in clients...