When some component in OP's dedicated server fails, they will find out what that extra DO money was going toward. The DO droplet will live migrate to a healthy server. OP gets to take an extended outage while they file a Hetzner service ticket and wait for a human to perform the hardware replacement. Do some online research and see how long this often takes. I don't believe this Hetzner dedicated server model even has redundant PSUs.
Anyone who thinks DO and Hetzner dedicated servers are fungible products is making a mistake. These aren't the same service at all. There are savings to be had but this isn't a direct "unplug DO, plug in Hetzner" situation.
Hetzner also offers a VPS with superior specs to their old DO server for €374.99/month, or €0.6009/hour. They could just switch to a VPS temporarily while waiting for the hardware fix.
Although since they were running a LEMP server stack manually and did their migration by copying all files in /var/www/html via rsync and ad-hoc python scripts, even a DO droplet doesn't have the best guarantee. Their lowest-hanging fruit is probably switching to infrastructure as code, and dividing their stack across multiple cheaper servers instead of having a central point of failure for 34 applications.