It's because of my workflow, I think.

I have my IDE open and a prompt a given task with limited scope - like "write a function that does xyz" "add tests" "create an endpoint that accepts this json" "write a sql repository for this schema" etc.

I use Rust on the backend so if it compiles it works, meaning I don't need to worry about runtime errors - if it looks right, it's right. On the frontend I use Angular, which is about as constrained an environment as you can get in the FE world, so it takes a lot to lead an LLM astray.

So my requirement for high intelligence is pretty low and I am able to review diffs quickly. Deepseek flash is extremely fast so it can render my prompts quickly - while Haiku, Opus and Sonnet are slow and create the same outputs.

I'm guessing the value of Sonnet+ is less hand holding letting you give it larger scopes of work? Giving an AI a high level task and letting it do its thing without needing to review the output?

I take that back, Haiku is considerably worse at following instructions compared to DeepSeek Flash