Don't understand lambda concurrency limit, 1000 seems ridicously low to me

As I understand it, at any given point in time there is a limit of 1000 lambda functions executing per region.
Based on my current application (not serverless), I expect to scale to an average of 100-400 web req/sec.
In my mind, each web request will have maybe 5-10 lambda calls through api gateway.
In this way, I will reach the concurrency limit pretty soon…And I will not scale any further.

So:

  1. I don’t understand well the concurrency limit
  2. my design is flawed, i.e. I should reduce drastically the number of functions needed to serve a web request (but then maybe they will execute for longer time?)

I’m trying to migrate an application to serverless and I’m struggling to understand if it’s the right choice

Here a couple of links I think you should read to get more details and resolutions how to prevent throttle error