I worked at a very mature software company (15k+ strong) for a couple years until recently. I was on a product team. The work was depressingly unfulfilling. I'm pretty sure I wrote less than 1k lines of code while working there. There's so much cruft - tests that break randomly, routine tasks not strictly related to software engineering, meetings, ticket investigations... If you find yourself in this kind of environment and seek excellence, I'd recommend switching.

Since then my preference definitely shifted towards smaller companies so I can get more experience working on greenfield projects.