I think you will find it's more than just theory. Where do you think antibiotic resistant bacteria get their start? From people who never take antibiotics or people that have taken them extensively? Or maybe people that start taking antibiotics and stop before the invader is dead.
Same with vaccinated people. Vaccinated hosts force the virus to adapt. Take a booster and the virus adapts again.
The vaccinated are providing a living laboratory for the virus to expand it's capabilities. Worse yet, no one and I mean absolutely no one knows what long term effects these vaccines are going to have on the human body. It's very likely these vaccines and their associated boosters are going to have a negative and permanent effect on our natural immune systems.
“I think you will find it’s more than just theory.”
Feel free to find a cite. So far you haven’t delivered and it’s not likely that you’ll be able to. The hazard of a little bit of knowledge breeding overconfidence.