It can help, but is not perfect. There's kind of been an arms race between services like Cloudflare and script kiddies/hackers DDOSing: Their methods became a little more sophisticated to the point that they keep the traffic shifting from address to address so it's harder to track/block.
They'll do other things to mess with the host too like spamming "white noise" pictures to fill up server storage space, so while DDOS attacks play a role, there are other issues at play on top of that.
For what it's worth, I've been using Kbin.social and sh.itjust.works as well and they have also had some issues here and there. No host will be perfect and invulnerable from every attack, and when an instance becomes more popular, it becomes increasingly likely to be targeted by attackers.