Does the way I website was built affect its capability to handle big amounts of load on its server?

I’ve been noticing in the past few days that a website built with .NET is less capable of handling a rush hour on its server(s) and it takes a long time to do anything when there’s a large number of users using it all in the same instant. However, I found that websites built with PHP or Python are much more tolerant to heavy server loads.

Is this really true? Or is it just my imagination?