Build something novel, what has changed?

I'd argue the question was wrong, it's not that big companies can copy you easier now. They could have always invaded your space and destroyed your business. As other pointed out it was always picking up the pennies that they didn't want until those pennies became dollars.

The concern now is that other small team or solo developers can rebuild what you have very quickly. This happened in the mobile space with all the decompiled and repacked (with min changes) apps that showed up in the stores.

The moat for SaaS startups was that the code is hidden. Now that matters less because people use AI to try and reverse engineer your backend from the API or even UI screenshots.

You have to pick up the pace to keep ahead of them and make sure you don't cause problems for customers while doing it.