I don't have severe myopia and I'm fine with no glasses for now. The optometrist detected .5 correction needed but advised me to not go for it for the reason I mentioned. I think they are more qualified to give this advice than some rando on the internet. If they were a mercenary they'd tell me to go for it, that optometry practice was part of an eye glasses store and I'm sure they'd gain from my business there. And here I am 20 years later not wearing glasses yet. As I'm getting older my vision is getting slightly worse, I'll probably get to wear them at some point but that's beside the point.
There is plenty of information about this in trusted sources, the way you're describing this is incorrect. Overcorrection and badly designed simplistic optics can make myopia worse in childhood when the eye is growing. Your eye is no longer growing.
Don't trust everything your doctor says verbatim, they often oversimplify and their information can be out of date. Give your doctor the benefit of the doubt but check it against other sources and use it to build a mental model.