Based on your experience looks like startup is a good match. The argument about learning the tools first doesn't sound that convincing to me , it is mostly you justifying the high salary. Also database is not a tool per se and even if it is you will mostly understand how to query it , which is just like learning SQL and I don't think it will help you in writing a database

‘Big Tech’ will always be there in some form down the road. If you have the risk tolerance and early career flexibility, take the path less traveled.

Go for the startup. You will have more opportunity to shine. With 2 yoe, you will get held back at Big Tech. Even if you know your stuff, the yoe will always be held over your head. At a 20 person startup, you will shine and be given more opportunity. This will bolster your resume and maybe even divert your career in a new and exciting way.

Big tech isn't going anywhere. If you are getting offers from big tech now, you will later as well. I always tell people to start at smaller companies. They are way better when you are young because you will face a wider array of problems, which builds better experience. Big Tech is great when you are older. It is generally more focused, higher paying, better benefits, but can often be less rewarding.

If you have never worked for a reputable big tech company, I'd do a brief stint for signaling, networking, and mentorship purposes. Then go to a rising startup.

Database startups really struggle because they compete with free and most database users need very little from their database. Enterprise customers do have advanced needs occasionally, but often it’s just about hoarding data or tracking users, neither of which does anything for society. Database startups are unusually hard because the real customers don’t want to pay and very few founders are able to get the hard tech right and are also willing to do the schleppy work of scaling up an enterprise sales team/process.