This is categorically false. If you have large capacity needs talk to your TAMs/Account Manager and they can make it happen.
It's been true five times in the last three years for me. The elasticity isn't always there and service limits are not always granted when needed.
I don't know what an AWS TAM is but the SAs have tried and failed.
Make a new account and try to run 1000 c4.4xl in parallel for 1 hour. It won't happen.
That's not what happened the five times, but it's illustrative.
And who defines what is a need and what is a want?
That's because of a history of bitcoin mining abuse.
People post their API keys on github every day and Amazon refunds almost all of the lost compute time.
I've asked and got basically a "no". I can believe that if you have a history of spending big $$$ on AWS they get increasingly flexible with raising the limits. But if you don't, they aren't going to let you spin up 500 instances, even if you ask nicely and have a reasonable justification.
Their service limits start low and ratchet slowly, if they have the capacity to give.
All these features and elasticity sound nice until you get big and they don't deliver.