at the bottom of the article they mentioned they hired 30k people to bring them up to nearly 190k last year, even if they perfectly fit in that's a lot of onboarding
That's actually low by Google standards, onboarding 16% of the company. There's been reports elsewhere that the average tenure at Google is 2.5 years, meaning a typical year sees onboarding 40% of the company.
40 % assuming a steady state of headcount. If they are growing, onboarding the growth happens in addition to that -- so 60 %.