There are still many use-cases where further control offered by open-source models (i.e. fully supporting all constrained text generation techniques) is superior. Stable Diffusion XL fine-tunes with controlnet, regional prompting, and the further extension ecosystem is still better than DALL-E-3 in the hands of skilled users.

But yes, the distance between the leading foundation models and the leading open source foundation models for LLMs seems to be getting farther, not closer.