Yes, if it was a wide-spread problem. The side-effect that killed AstraZeneca wasn't widespread, it was extremely rare, and it was caught because it was such an unlikely combination of symptoms. Yet, this extremely rare side-effect was enough to make the vaccine more dangerous than the virus - to young women at least.

In a year, when all the facts are collected and processed, we'll see how much trouble the Pfizer vaccine really caused in terms of Myocarditis. Then we'll scramble to make up numbers on how many infections must've been prevented by the vaccine to make it all worthwhile.

...like COVID in young people?

It's true that Myocarditis often goes unnoticed and undiagnosed. That's what makes it dangerous. It's a leading cause of cardiac arrest in young people. If you actually do get diagnosed with Myocarditis, it's not necessarily a mild case. That's what makes me suspect the cases being reported now are just the tip of the ice berg.