> There's no a priori reason why the expected success rate of research projects should be 50% and not, say, 1% or 99%.
Humans are really bad at predicting the future, so I'd argue that the large majority should be between 49% and 51%. A 99% success rate would imply that humans can predict the future, which I think is pretty much the opposite of how science should work.
I would actually put it 60-80%. As there is plenty enough of ideas that should work. It is not really random search, but applying existing knowledge or expectation to some different area. If doing one thing with one thing works, I would fully expect in many cases that doing same thing with this other thing relatively closely related to also work.
Lot of research is iterative process and there you can do iterations that you know could work and already ignore things that certainly won't.
