Codex vs Factory vs Cursor: Does the Harness Really Matter for MVP Prototyping?

Claude Code vs Factory.ai vs Codex vs Cursor meets GPT 5.3 Codex v Opus 4.6, who wins if the prompt and skill is same? What does it matter if you use Claude Code or Cursor? or Factory? Does it even matter if you use GPT 5.3 Codex for all your tasks?