No, it is not valid, and I will explain it perfectly: you are thinking that on an INFINITE time scale, even if custody techniques improve, eventually you could lose it all. However, the losses are not additive, but percentage-wise -- it's like a shitcoin down 99%, it won't go up, it will just fall 99% again. So you can lose bitcoin forever, and since it is about the distribution, and it is held across a large number of independent actors, you never actually approach zero in the way you are imagining.