I ran 5 now famous companies' ooriginal pitches through a brutally honest idea-validator. It rejected 4 of them

I have been building a tool (with agentic capabilities) that gives critical, honest feedback on startup instead of the usual "great idea, you've got this." To see how honest it actually was, I fed it the original pitches for 5 companies now worth billions, written the way they really sounded at the start.

- Airbnb: "Rent an air mattress in a stranger's home." Result: Don't Build it, 2/10.

- Burbn (Which became instagram): A check-in app doing photos, plans and badges all at once. Result: Don't Build it, 2/10.

- Slack: Another team chat app. Result: Don't Build it, 3/10.

- Stripe: A payments API. Result: Don't Build it, 3/10.

- Dropbox: A folder that syncs. Result: The only one it did not kill Test it first, 4/10.

At first I thought the tool was broken. Then I realised it was not wrong, it was reading them the way the market actually read them at the time. Almost every investor passed on Airnbnb. "Just use rsync" was the comment when Dropbox launched. The honest read of the raw pitch genuinely was skeptical.

Two things stuck with me.

Survivorship bias is brutal. We only remember these as obvious because they won. The original pitches really did look weak, and most ideas that look like them do fail.

What separated them was not the idea, it was the one wedge each found later. Airbnb's was trust and reviews. Instagram's was deleting every feature except photos. The tool actually pointed Airbnb's trust gap and at the too many features problem in Burbn, which I did not expect it to catch.

It made me think the useful question isn't "is my idea good", It is "What is the one thing that would have too be true for this to work, and how do I test that this week?"

I am curious what other people make of it>? Does an honest no on the original Airbnb pitch mean that this tool may be dumb? Or actually was the pitch that bad until they found the edge ?