I don't think subs are what keep their lights on. And their API is so absurdly expensive. For the harness hard disagree but ultimately its up to each ones taste. You may want to check this tho https://harnessrank.net

On our side we use Claude/GPT/Kimi (it replaced Antigravity) for development. But we build our systems around a cheaper denominator (Deepseek previously, recently we added GPT 5.6 which have good prices as well). We offer BYOK for Claude but its def not an option to build something on top of it (for us).