[mful]

Engineering learnings at big cos vs startups are wildly different. If your goal is to learn what it takes to start your own company, you are much better off working at even a mid-sized startup, than a big tech co. There are a number of reasons for this, but a particularly consequential one is that you will learn to build/manage/deploy applications from 0, and if things go well, through a variety of scales thereafter. At a mid-size startup you'll have less of the "from 0" bit, but you are much more likely to learn to deal with the scaling issues that manifest as the software that was built in the early days starts degrade with growing load. You will also likely be using similar open source tools in both the early & middle startup stages.

Building features in a large, existing codebase, in the robust tooling context of a big company, is nothing like building services from the ground up.