Andrej
I would agree with you, if there where no signs of arming. But this is not the case. We have a green LED that shows you the state of arming. Furthermore you GCS is TALKING to you. If this is not enough, you can read out the mavlink messages and add some extra LEDS or a beeper (with mav2hott).
Best
Christof
BTW, I had some experiance with accidentially rotating props. It took 12 stiches to get my forearm back in shape. And it was just a sailplane with 0.5kW, throttle @ maybe 25%. I do not want to imagine what would have happend with my 4kW Mustang or the 4.2kW TRex 700.