Similarly to how 90% of my LLM needs are met by Mistral 3.1, there's no reason to use 4o for most t2i or i2i, however there's a definite set of tasks that are not possible with diffusion models, or if they are they require a giant ball of node spaghetti in comfyui to achieve. The price is high but the likelyhood of getting the right answer on the first try is absolutely worth the cost imo.