Very fair question! There have been some changes since then. The first is that prioritization is being changed. Back then, to be totally honest, prioritization didn't work well. We thought it did, but it didn't. Back then prioritization was done through a client-side PoW that was performed - more PoW performed, more priority.

Nowadays prioritization is based on time since last transaction and balance (see also https://senatusspqr.medium.com/nanos-latest-innovation-feeless-spam-resistance-f16130b13598). This doesn't mean spamming is impossible, but it should make the impact for real users far, far lower.

As for your specific questions - the blockchain is secure. There was never a doublespend, never any doubt about transactions, they were just delayed (and were mostly still way faster than Bitcoin transactions, for example). One person can ask for things in every network, and people can listen to them. In this case, throttling seemed like a good idea to many node operators, so many (though not all) did so.

Comparing it to Bitcoin, there are sometimes updates published, and every node operator can choose whether to upgrade or not. Nano works the same. There's no central authority that can force anyone.

Hope that helps!