That’s nice that the PCR technique was accepted by scientists. The tectonic plate theory wasn’t. It took decades for scientists to accept it, and most of that was due to the dictum that the scientists who were against it basically died off and a new generation of people were more open minded. Similar thing happened to LENR. Rossi’s device is just the latest development in LENR.
There are a few key differences here.
The theory of plate tectonics was developed by actual scientists who understood the physical basis of the observations they used to develop the theory. Rossi is not a scientist, and has not demonstrated that he understands anything of the physical principles he claims to be applying here.
Scientists who have developed theories which are slow to be accepted (and there are actually a few examples of that) never try to hide the data; they make it available for anyone to inspect. They also describe their methods so that other scientists can replicate the experiment and verify the data for themselves. Rossi has been ultra-secretive, has not performed a single experiment that would support his claims, and will not allow others to do those experiments. He could do a lot to silence skeptics simply by doing a few simple experiments and allowing independent researchers to test his device.
Anyone can claim to have achieved anything. Without evidence, such claims are meaningless.