There are a couple of variables why it would be slow for you. Steam sharing works great as long as:

Host isn't downloading something
Client isn't downloading something
Client has a fast CPU to still unpack the game
Client has fast storage to saturate the network speed
Host has good network speed
Client has good network speed

For me, it really is that simple. It sometimes even works better than the server cache setup

Note though, you really need a FAST CPU to unpack steam games at even gigabit. It will also make bad SSDs cry.

Can you do it again and share that graph? is the green line higher than the blue bars?

I didnt even know there was trackers for 3d printing. Does materialize have any public signups / interviews?