Sure there are breakthrough cases, but if you are unvaccinated the chances of catching covid are still much higher. And if you get myocarditis with the vaccine (which is rare) you will get it much worse with covid.
Actually, data from the only places which break this stuff out properly (like the UK) shows the rate amongst vaccinated people is massively higher than the rate amongst unvaccinated people. It's been like this for quite some time. Effectiveness is sharply negative by anywhere between 50% and 300% depending on age group.