I'm not questioning that PhD programmes infuse skills/knowledge useful in big tech but I wonder if here we're are also looking at useless grade/degree inflation

I'm not questioning that PhD programmes infuse skills/knowledge useful in big tech but I wonder if here we're are also looking at useless grade/degree inflation. Surely if there's surplus of "overqualified individuals" it becomes cheaper to hire them. Is it net cost effective for all that this is the case? Do you really gain so much by wasting(?) 3 to 5 years in a PhD programme?