I've tried smaller models and the best open models for a specialized UAV focused CAD + CFD + DFM optimization application I'm building.

The best open weights models still had a lot of defects and very egregious mistakes to fix even after I provided a very well detailed Requirement/Design/ Technical Implementation plans.

Opus and Gemini 3.8 (and now Argon) did a significantly better job. So I've baseline using these two models to build this application. I now use Opus for design/review and Flash 3.8 for the code gen/implementation work.

I'm sure small models and even open big models are probably fine for many common small apps and such, but they aren't really able to perform the same across all use cases.