It’s not a technical problem, but a systemic one. Getting way too big relative to the rest of the fediverse paints a target on your back. There is a reason your instance is being DDOS’d while so many others aren’t and one instance being DDOS’d shouldn’t be have such an impact on the overall system.
My point is that the sensible thing to do would’ve been to limit growth of .world and let others catch up. This is what the lemmy devs did with their instance, this is what Hugo from masto.host did to his service (stopped accepting new customers when he got close to 50% of the users) and this is even what Eugen did with mastodon.social and mastodon.online in the beginning.