tomw, 
If a few hundred simultaneous requests can bring down your website, don't moan about Mastodon instances for sending them. Fix your website.
This doesn't need to be a big job – for most servers it's a couple of config lines, plus for Wordpress or similar you'll likely need caching.
It will prepare you for the day when you publish something that gets a lot of (genuine) traffic.
This level of traffic is not a "distributed denial of service", it is a "small-to-medium-sized request for service".