Do streaming apps use Wifi or X1 box?

Trying to figure out how streaming apps work in the X1 environment. Does the stream come through the X1 coax to the box out the HDMI cable to the TV or does the streaming app communicate directly with the TV via Wifi? 

1. Select a streaming app from the X1 remote: In this case, I am connected to "Comcast HDMI" viewing cable (and live TV). I now want to watch something on, say, Hulu. So I the click the Xfinity button on the remote and then select the streaming app.
2. Select a streaming app from the smart TV menu: After powering on the TV instead of connecting to "Comcast HDMI" I select a streaming app from the smart TV menu, say Apple TV. 

I'm trying to get a handle on why some of the streaming apps are painfully slow (here's looking at you Paramount+ and Prime) while others (Netflix, Hulu, Peacock, primarily) work just fine. If Wifi, I can sort of understand because even though I am paying for gigabyte speed, my Wifi speeds are pathetic. (Sometimes sub-100 Mbps to at best around 300 Mbps as measured by Xfinity speed test and Ookla, including standing right next to the gateway with a tablet.) Of course, on my ethernet connected Mac, I get 900+ Mbps so no issues there. Is the solution simply to connect the TV to the gateway (ethernet)? Just not sure why some streaming apps are so very slow or unusable while others are fine.