Yes, if your elasticity requirements are not within hours but within weeks or months, adding and removing capacity can be done by traditional means, even by renting physical servers and putting them into your on-premises racks.

You missed the point - for some the 'elasticity' is just being able to consume 12-20GHz instead of ~1-2GHz 350 days of the year. Sure, you can deploy some advanced hyper-scaling arch to do so... or just move to a fatter instance.