I have a Gtx 1070 and an i7 8th generation and 32 Gb Ram.
In Fortnite I have everything low continuously around 160FPS.
Own According to Youtube / google I should have 300-400.
Why is that?
Did you update the latest graphics card drivers?
If you have a 60hz screen or even 144hz screen, the 300-400 fps won't do you anything.
Then they probably play in a lower resolution.
Check out Task Manager for your workload and, if necessary, close all programs in the background that you don't need. Then go to autostart and deactivate everything that is not important or should not start when the pc starts
"Youtube" is not such a great source. It can be random or a serious channel, we don't know. But you can read here how much a 9900K on medium can do with your card, namely about 160FPS:
https://www.fpsbenchmark.com/fortnite/gtx-1070
