That's what works for products, not software systems. Gradual growth inevitably results in loads of technical debt that is not paid off as Product adds more feature requests to deliver larger and larger sales contracts. Eventually you want to rewrite to deal with all the technical debt, but nobody has enough confidence to say what is in the codebase that's important to Product and what isn't, so everybody is afraid and frozen.
Scale is separately a Product and Engineering question. You are correct that you cannot scale a Product to delight many users without it first delighting a small group of users. But there are plenty of scaled Engineering systems that were designed from the beginning to reach massive scale. WhatsApp is probably the canonical example of something that was a rather simple Product with very highly scaled Engineering and it's how they were able to grow so much with such a small team.
Scale is separately a Product and Engineering question. You are correct that you cannot scale a Product to delight many users without it first delighting a small group of users. But there are plenty of scaled Engineering systems that were designed from the beginning to reach massive scale. WhatsApp is probably the canonical example of something that was a rather simple Product with very highly scaled Engineering and it's how they were able to grow so much with such a small team.