I appreciate your frustration. A couple of things I've done to alleviate some of the challenges:
1) After trying to use WiFi to control the RPi, including adding external antennas, I finally just used a long ethernet cable to connect the RPi to my network. I think that is what Alessandro meant - not a cable from the RPi to the device with the app. I'm sure the bad RPi WiFi support is why ZWO's ASIAIR now has external antennas. My experience using WiFi was the same as your - almost unusable. Ethernet has been solid.
2) While I don't do EAA, I think Alessandro is correct (I'm sure other's will chime in) that, when you use Stellarmate from a mobile device, the computations and such take place on the RPi and are displayed to the app - can be very slow. I know that when I went to a full frame camera, I also had to change the RPi to an 8GB model - the 4GB was unusable. What I have switched to is just running the Indi Server on the RPi (that comes with the StellarmateOS) and running KStars/EKOS on a laptop or desktop computer - that way most of the work occurs on a more capable device.
I think the UI on Stellarmate is evolving in good ways but the mobile device control of the RPi is hampered by the lack of power in the RPi units and their bad WiFi.