The only decentralization that's going to work is actual decentralization where there's not really anything to DDOS, or rather the entire system is itself a botnet.
There’s always something to DDoS. It comes down to whether the attacker has more resources than you have server capacity, and these days attacks can be measured in terabits.
Well, every service that gets ddosed was once a service that nobody cared about.
But if your service is in a category that attracts ddos (like a forum or game) and you ever get enough traction for someone to care (doesn’t take much), it might surprise you how cheap it is to take you down and how limited your options are against a simple volumetric attack.