So... every company only hires the best!? I jest, I jest!

In general, I've found that the younger engineers (20s, up to 30s) have a lot of vim & vigor; but, even the very best ones generally do a lot of spinning-in-place, when they think they're making progress. Almost anyone above a certain level -- call it the 30–40% mark (it's low!) -- can be raised up to be a competent engineer. Probably what'd be called an "an A- or B+" player? That's just part of a good training & onboarding regime; although, it can take 1-3 years, depending on the person. Very good "natural" talent can definitely boost top performance to an A+, but it won't substitute for literal time-under-stress of delivering high quality product-ready code to clients.