If a decentralised system is to stay decentralised, it needs to consider spammy bad actors.
Also, it was only up to like very early 2000s when researchers of decentralized systems mostly ignored the existence of malicious actors, but later everyone became well aware of them and started considering how to deal with them.
But in practice datacenters, uplinks and internet exchanges often are able to do flowspec, firewall rules, block all UDP for a subnet in all networks they have relationships with, etc. So plenty of those nodes can be behind ISPs that mitigate volumetric attacks automatically, so even simple DNS failover might be good enough to protect from such attacks. It's not that hard. Layer 7 is where the hard part is.