Why is my T Mobile phone hotspot getting more consistent internet than my 5G gateway

It depends on hardware, and maybe other factors.  My OnePlus 9 and OnePlus 12 both get smoking fast 5G in certain locations, including my home.  Those phones have flagship chipsets and antennas.  The 5G GW probably has lower performing SoC and specs say omnidirectional antennas.  The phones and other devices use beam forming to compensate for continuously changing phone orientation.  Omnidirectional doesn't sound like beam forming to help with direction.  My phones get about twice the data rate of the 5G GW, all generally exceeding 150 Mbps, usually >300 Mbps.  I got the 5G GW assuming it would get smoking fast data at home like my phones.

Location matters though.  Many locations have far lesser performance on my phones, so I assume the same would apply to the 5G GW.

The GW also has 4 antenna connections to in theory use antenna that would be high gain and could be optimally directed (versus omnidirectional).  I have no experience with that; only what I've read.  I don't even know what options there are for getting such antennas.

The so-called "mesh" device, shaped like a pancake connected to the GW with a wired coonection, which T-Mobile wants you to get at extra cost, is for helping WiFi coverage around the house.  Like using a WiFi router in access point mode, connected by Ethernet cable.  Despite what folks have told me, I seriously doubt their communicates with T-Mobile 5G, or even some "Starlink like" satellite communications.  People state things they don't know accurately (store reps?).  It just helps with local Wi-Fi, probably Wi-Fi 6.

Thats about all I know  so dont rxpect more help from me.  I don't know more.