If you’re looking to be impactful, you are much better off joining a job and working in your free time, than doing a PhD. A PhD is a program to compete for academic prestige. Grad students want to publish papers that get them noticed at conferences, invited to talks at prestigious universities etc, those are the incentives, always has been in academia. The brightest minds join academia because they care more about prestige than money (as they should, anyone can earn money, few can win a Nobel prize). In a healthy academic system, prestige is linked to real world societal impact. That is still somewhat true in fields like Machine Learning, in some fields it seems to be completely dis-aligned from any real world impact whatsoever (which seems to be PL research). Our academic system unfortunately is a rotten carcass.
You could still, advisor willing, do research that interests you and not care at all whether you get noticed by conferences/ journals, your peers etc. But that takes a certain level of anti-social behavior that very few humans possess and so I say join a job. Plenty of companies are still building programming languages, like Google, Apple etc which are being used by engineers worldwide and if you finagle your way into a job at those teams, you will have a meaningful, impactful job, which is also well paying as a side bonus.