Almost every operations manager I know is either a chemE or ME who started off working as an area supervisor over plant operations. Ditto to plant managers. My dh has always worked in the process side of operations or in technical sales. He has been part of international plant joint venture start-ups. Our ds, otoh, works in operations.
Fwiw, I asked my dh and he said, yes, it has been that way for every company he has worked for over his career.
And he said that they do “mix chemicals” but in terms of 1000s of lbs, not at all like a lab.