That's not how it works since each instance can handle multiple requests (up to 1000 per instance). So you may set this to scale at say 75% load level.

Indeed if you configured each instance as a single threaded handler, you will not have fun.

That's only how it works when misapplying mean() to characterise application performance. In your scenario, every request is hitting either an overloaded instance, or when scaled down, a 20-30 second wait for spin up, better hope they're neither interactive nor some jobs configured with a short timeout. The mechanisms are so completely different they're hard to even make meaningful comparisons between