Xbox(s) download speed much slower then any other device on network?

Try to calculate if it is downloading at a normal speed and only the mb/s shown are wrong, or if it is going slower. That’s because when it says 300 mb/s it is actually going much slower because the server you are downloading from have a max quantity of
data provided per second.

Is it any slower on pc?

If you are using various devices on the same network it may cause slower speeds for your Xbox 360. Try downloading something with only the 360 connected to your network and see if that speeds it up

Internet speed is affected depending on how many devices are connected on that network at the same time, the 10 megabytes of your connection are distributed to all devices, and connections become slower. It is recommended to use a wire to connect the console,
since it is faster than WiFi. Also sometimes game downloads are faster other times slower although the console is connected by wire.

I always get a much greater download speed on my Xbox One than I do on my PS4 or my Switch. Only my PC gets better download speeds out of all of the formats that I use. Sorry to hear that you're having issues though, if you've only got slow speeds on your
Xbox and not on other devices then you may have some network connectivity issues.

This link may shed some light on the problem:

https://support.xbox.com/en-US/xbox-one/networking/slow-performance-solution

I'm the opposite. My PS4 downloads faster than my X but slower than my original One.

Your download times will depend entirely on your home network. If you have low download speeds, or many devices all connected at once, this will significantly worsen your download times.

The games are also considerably bigger than their 360 counterparts (40GB on Xbox One versus the typical 5-6GB on Xbox 360), which will also make it seem like it's much slower than you're used to.

You can check your download speed by going to Settings/Network/Bandwidth Usage/Current Usage. This tells you your download speed and by knowing the size of the game you can calculate the expected time to download.