Not convinced
I'd like things to play out the way the author suggests, but unfortunately, I think he's wrong while I want him to be right.
AI does do a lot of what juniors do in many professions, including making lots of mistakes. The real debate is by the time today's juniors become tomorrows seniors (actual seniors not juniors with 5 years experience and a wholly inappropriate job title), what will AI have become? For some, perhaps many, roles its not inconceivable that it'll be capable of doing senior level work and so the need for seniors will have been reduced or absorbed.
Translators, for example, will never be needed in anything like the same quantity as before AI, if at all by the time a junior translator hopes to become a senior translator in say 15 to 20 years.
In terms of software engineers, its very hard to argue that AI hasn't outpaced its entire cohort of junior devs in terms of quality of output. There's a credible argument that it won't continue to do so, but there's an equally plausible argument that it does. While personally I think there will still be a need for senior engineers, there is a limit of how much money I'd want to bet on that. What if, instead of investing in todays juniors, a business saves that cash (literally) and uses it to fund hiring tomorrows scarcer senior staffer? There's no reason to think that those investing in juniors will reap any reward when they become seniors because they'll go for the money, same as everyone else.
The hype around AI is well overblown, for sure, and its definitely not going to be all things to all people, but there are a lot of careers never coming back, and there's a lot more still that won't require the same volume of people to do the same level of work. Marketing, basic accounts clerks, etc won't be needed in future at anything like the level of employment they've enjoyed previously, and for sure the same is likely to be true of some tech jobs also.