I think there are two types of startups and it depends what you are actually doing:

- Startup that has product market fit (or is really close), and is ready to scale: choose boring tech that works

- Startup that is a playground, exploring or building new tech, and may never make money.

You can join either as an employee/cofounder/leader, and have a great time, but if you mistake one for the other, you will have a bad time.