You can fly w/o the esc ubec feed to the fc. Normally the purpose for it is 1] to supply a backup power source to the fc in case something happens to the normal power supply, and 2] to provide a powered rail that you can use for other devices.
That said, as of late I use an independent ubec from the pdb and not the esc. I use it to power other devices such as range finders, LEDs, optical flow, etc. I still use the fc telemetry to power the RPi and so far haven’t had an issue, but I recognize an undervoltage could occur.
I cannot understand why your RPi would draw max amps for simple flight missions unless you also had some special devices on it.
I once had one of these escs catch fire on a hard landing, presumably because it was putting a lot of current through to manage the motors and fc. 50C is close to where it can burn flesh but normally not close to ignition temperatures. Once airborne I would assume it cools off - you can put a temperature sensor on it and see. But these escs are cheaply made but low price. So always keep a fire extinguisher around when you fly.