You can do that (building apps on LN) in many ways:

- run a private node connected to a good LSP / public node

- run a public node with 4-5 good channels only, with good peers, as a decoy for a private LN node dedicated to your project

Nobody says that first you have to be profitable as LN node in order to build your project. But you have to take in consideration why somebody else would open a channel with your public node.

For example, I see Rizful (disposable) nodes perfectly fine for a small project. With just 1 or max 2 channels, well positioned, it is more than enough to have some liquidity for building a project. You can run both public and private channels on it.