A booking site on Wix Velo timed out under launch traffic, and the bottleneck wasn't the design.

A booking site on Wix Velo timed out under launch traffic, and the bottleneck wasn't the design.
They built a class-booking platform in Wix with Velo code for the logic. Launch day brought 4,000 concurrent users; backend functions hit execution limits and bookings started failing at the worst possible moment. They moved the booking logic to a small serverless API and kept Wix only for marketing pages. Next launch handled 9,000 concurrent with zero failures and median response of 240ms. The lesson costs more than the fix: builders are great until the thing you're building is the load-bearing part.
Agree? Or am I wrong?