There's a distinction between just saying it's more expensive and saying it's slower at the same price. Compared to well spec'ed and administered dedicated servers, it's basically impossible to get the same performance from AWS (or other cloud services) at any price. Yes, there are advantages, scaling being the greatest one. But you won't get the same raw speed you can achieve with fast storage and processing in a single machine (or a tight network) through cloud services—probably at all, but certainly not for anywhere near the same price.

And if you are willing to pay, you can significantly over-provision dedicated servers, solving much of the scaling problem as well.