Your point is valid legally. And in many cases you’re right, your options are limited if someone isn’t driving correctly near you. However I still disagree on the idea that there’s not much you can do to avoid situations if you stay aware of potential problems. That’s where defensive driving comes in - if I see someone is following too close in traffic or isn’t slowing even though I’m signalling a turn, I’m not going to take a position of “well, I’ve done all my legal required actions, it’s out of my hands.” I’m going to use the outs that I’ve already got in my head to avoid them hitting me, whether that be changing my speed to space out the reaction time for them, abandoning the turn or move, or going off the road.