Slow download while the app uses all the internet speed

[lietuvis3]

Hello, I have recently built a gaming PC and the download speed is quite problematic. My internet speed is 50/10 and I'm using an ethernet cable.
The specs are:
CPU: i7-8700
GPU: ASUS GeForce GTX1080 8GB ROG Strix
mobo: ROG STRIX B360-F GAMING
RAM: Corsair Vengeance LPX DDR4 2666MHz 16GB
SSD: Samsung PM981 SSD 256GB PCIe M.2
HDD: Seagate Barracuda 1TB SATA3.0

If i open my task manager i can see for example steam using 40-45 mb/s of my internet and I'm downloading games at 6 mb/s
If i plug the cable into my old PC it downloads games on steam at 40 mb/s and that computer is a trashcan. best piece of hardware in it is a gt 730...

I have googled for a couple of days but found nothing adressing the same issue. It is not only steam but Epic Games launcher, uplay, origin, leauge client. Even when i throttle the steam download speed to lets say 5 mb/s it still uses 40-45 mb/s and no once can use the internet at my house.
Now my knowledge about internet connections is not the best but i dont understand how getting a better mobo than the previous one the internet fu**s up.
Help please

 

[velocityg4]

Steam shows download speeds in MBps (megabytes per second). Task Manager shows network speeds in Mbps (megabits per second). There are 8 bits in a byte. Steam working at 6 MBps is equivalent to 48 Mbps.