Please. Captcha by default. Email domain filters. Auto-block federation from servers that don't respect. By default. Urgent.
And yes, to refute some comments, this publication is being upvoted by bots. A single computer was needed, not "thousands of dollars" spent.
If they choose not to take measures against bots defederation is the only way to keep that wave out of your own instance.
Do not make assumptions on how other instances are operating. You don't know what measures they're taking. If they did not cause you trouble yet, don't try to predict it by making generalizations. It creates an echo chamber Internet.