the original virus is hundreds of mutations old by now.

You make it sound like they all mutate at the same time into the same thing.

Some copies of the virus mutate, most don't. Most mutated viruses aren't viable, and they perish. Just a few live and many of them are weaker than the original. So only a few mutations are worse than the original, like the delta and lambda variants, but they are more transmissible and more infectious so they spread more rapidly and do more damage.

There's still some of the original covid virus around but it's being outpaced by the new ones, especially among the unvaccinated.

Fortunately the vaccines have some effect on the new variants but that may not always be the case, so the sooner everyone who can be is vaccinated the better off we'll all be, cause that's when the production of variants will slow down.

the original virus is hundreds of mutations old by now.

You make it sound like they all mutate at the same time into the same thing.

Some copies of the virus mutate, most don't. Most mutated viruses aren't viable, and they perish. Just a few live and many of them are weaker than the original. So only a few mutations are worse than the original, like the delta and lambda variants, but they are more transmissible and more infectious so they spread more rapidly and do more damage.

There's still some of the original covid virus around but it's being outpaced by the new ones, especially among the unvaccinated.

Fortunately the vaccines have some effect on the new variants but that may not always be the case, so the sooner everyone who can be is vaccinated the better off we'll all be.