I did not choose DeepSeek because I think GPT-4 is bad. I chose it because I was building a free app, and free apps teach you what actually matters pretty fast.

The question was simple: how do I keep sessions cheap enough that people can practice a lot without me lighting money on fire?

The answer pushed me toward DeepSeek-V3 (and later R1 for specific tasks).

The real constraint was volume

The app is a conversation practice tool. People come in to rehearse hard talks, not to admire the model.