tmobile wifi gateway vs connecting with google nest mesh

I've had my gateway a little over a week. I started out just plugging my existing mesh network into the gateway. I noticed that when I connected to the gateway's Wi-Fi the speeds were in the high 300s. When using the mesh Wi-Fi it was in the mid 100s, so basically half. I'm trying to find a way to extend the gateway's network using my Nest mesh system instead of having two networks.

For the record, the gateway sends a signal strong enough that I'm able to access it from anywhere in my 1200 sq ft apartment. I've never had that ability without a mesh system. The only reason I need to keep the mesh is because there are devices in other rooms that need to be plugged in to an ethernet port.