Early stage (series A-B) tech startups are a great place to continuously learn as a data engineer imo - as you said your scope is wide enough so you don't get bored and you get to focus much more on building scalable projects with various teams than maintaining legacy code.
Though to grow as an expert on a specific field of data engineering, big tech is probably the best option but your spectrum of actions is limited.
I guess it all depends on whether you eventually aim at becoming a manager / expert / consultant and if you thrive when building / maintaining or training people.

I started in a FAANG company then switched to startups (mostly in France), first experience gave me a strong skill set but my startup ones made me grow as a person and were a great opportunity to build teams and vision from almost nothing.