1. To optimize an existing product
2. To build a new product
I have the answer.
The thinking was flawed. Optimizations are good, but they only bring incremental value to the company. Product innovation takes time, but if done well, it brings 3X - 10X value for a company once released.
Beware that you will reach a limit on growth through optimization, so always be innovating.
So your startup is not any different from a big company if you do not invest in product innovation.
The promising startups that never became as big as you thought they would abandonned product innovation for optimizations.
However, releasing new products comes at high risk. The assumptions you made when building this new product could be wrong and you might lock up scarce engineering resources for 3 - 6 months.
If you pick product innovation, make sure the product improves the experience of the user.