To be fair - you're getting maybe $75 worth of hardware, plus datacenter space, power, and an unmetered 200Mb/s network feed to it - none of which you can get for free even if you have a spare 'Pi and SSD lying around doing nothing.
It's no great saving over places like Hetzner or Digital Ocean, but I don't think it's _quite_ as bad a deal as you're making out... I wonder how much more than $300 it'd cost you to buy the hardware that Hetzner give you for four times as much per month?
"I'd rather pay four times more for something better" isn't the most compelling argument against Scaleway. They're targeting people who want to host something for $10/month. For the money what they're offering is pretty good.
except the raspberry isn't in a datacenter, it won't probably have the same network speed, you can't move an IP from a raspberry to another one, you can't easily make snapshots, ...
On their premium bandwidth Scaleway do. Hetzer however provides no such protection and does not assist with mitigation whatsoever (other than null routing your server until the attack stops).
Just look on the various web hosting forums (webhostingtalk.com) with regards to Hetzer. They are very hostile to customers that have these problems.
OVH, which are priced similarly, include DDoS protection in all their new plans.
I find Hetzer are good for non public facing servers. Job processors, internal tool servers etc.
For the best protection you need to pay more - in the case of Scaleway, their pricing page (https://www.scaleway.com/pricing) says it's available with the "premium" bandwidth option - but anecdotally I've heard even the basic protection is pretty good.
I rather pay $40/mo for Hetzner 3930 CPU server with something like 30 VMs.