You seem to be setting a high bar (AI success stories don't ring true), while taking the study as fact. This feels like a cognitive bias.
I believe you are talking about the study: Measuring the Impact of Early-2025 AI on Experienced Open-Source Developer Productivity. It is an interesting data point, but it's far from conclusive. It studied 16 developers working on large (1MLOC+) codebases, and the AI tooling struggles with large codebases (new tools like Brokk are attempting to improve performance there). The authors acknowledge that participants dropped hard AI-disallowed issues "reducing the average AI-disallowed difficulty". Some of the selected developers seem to have been inexperienced at AI use.
Smaller tools and codebases and unfamiliar code are sweet spots for the AI tools. When I need a tool to help me do my job, the AIs can take a couple sentence description and turn it into working code, often on the first go. Monitoring plugins, automation tools, programs in the few thousand lines of code, writing tests, these are all things the AIs are REALLY good at. Also: asking questions about the code.
A few examples: Last night I had Claude Code implement a change to the helix editor so that if you go back into a file you previously edited, it takes you back to the spot you were at in your last editing session. I don't know the helix code nor Rust at all. Claude was able to implement this in the background while I was working on another task and then watching TV in the evening. A few weeks ago I used Claude Code to fix 600+ linting errors in 20 year old code, in an evening while watching TV, these easily would have taken a day to do manually. A few months ago Claude built me a "rsync but for block devices" program; I did this one as a comparison of writing it manually vs vibe coding it with Claude, and Claude had significant advantages.
But, I'm guessing these will fall into the "does not ring true" category, probably also "no real objective validation". But to me, personally, there is absolutely evidence that AI is actually getting things done.