Need some help on setting up and understanding AP

Ok, so I have a TMobile gateway that was plugged into a a router running wrt software. I originally had the wifi for the gateway turned off and allowed the router to transmit. Speeds were horrible. I saw a post about AP and decided to try it out. Here is what I did, hopefully correct, and if so, can someone explain whats actually happening?

The SSID of the gateway is X2 and X5 for both 2 and 5g. I plugged the gateway into the lan port, not internet port on back of router. I have other devices that are not wifi and they are also directly plugged into the remaining ports. The router, was set to the instructions here:

The router has the same SSID and pw as the gateway. Everything seems to be working and the speeds are super fast now. Am i pulling the SSID off the router or gateway, both? Should I disable the wifi on the gateway or router? Thanks for the help.

That will allow roaming to occur (i.e. your clients should roam to whichever has the best signal performance).

One at a time, but in theory both (per the above comment).

If the two devices are relatively far from each other (i.e. different rooms, etc.), having both enabled will allow the client devices to use the one with the best signal. If they're close to each other, though, then there is no need or value in having both running. In that case, try turning off wifi in the tmobile gateway and see how things work. and you can test the other way, too... if you find that the tmobile gateway alone provides sufficient performance, you don't need the other AP.

Thanks. The router is about 4 feet away from the gateway. Ive disabled the gateway, then the router only, in the past, and other configs, but the speed frankly was crap... this is the only instance where the speed has been lightning fast... I wonder if I should just let it be... lol... thanks. I guess no down side?