Geri said:
relying on it will be magnitudes more fast, secure and reliable than a hand-crafted solution in your program

Nobody said you should put it in your program. My point is that, if the packet already made it to your server machine, you already lost – the link into your machine is saturated. You must block DDOS traffic upstream.

Geri said:
The second is the speed of the internet. 10 mbit/s

I'm sorry to hear that.

Half a year ago, the median US bandwidth was 167 Mbit/s download, with another five countries being faster: https://www.allconnect.com/blog/us-internet-speeds-globally#:~:text=According%20to%20Ookla's%20Speedtest.net,for%20median%20fixed%20broadband%20speeds.​​

The global fixed-wired is 75, and the global hard-wired is 36: https://www.speedtest.net/global-index​

Geri said:
assuming everyone will have 10 mbit isnt true either

How much bandwidth you want to use, depends almost entirely on what your main target market is, and what it'll take to deliver the gameplay you want to deliver.

Just like when you have a CPU requirement, a GPU requirement, a RAM requirement, a display resolution requirement, a hard disk speed requirement, … you need to figure out what you want to deliver, what it's going to take, and how big that market is. As you start optimizing, the amount of time needed goes up steeply, and the number of additional users you will reach will taper off, so there is a sweet spot in “return on investment” where not everybody can run your game. Such is life; we have to make rational choices!

If your game is a turn-based games, clearly you don't need to send a gross of packets, each with a dozen kilobytes of payload, per second. Different games have different needs!