Well, you can run Nostrsync and the content is distributed across a lot of relays. For this particular problem, it is not about "there are 6 big relays", if you want content deleted, you need it deleted everywhere, which is difficult to do.

If all of them were taken down, the network would not work well. But the other way is not so easy - if you want to take down a note, you need to take it away from all relays and with nostrsync, this is very hard to do.