I largely agree with what you're saying but I'm going to add... If you get to the point of release and you're off 300% and not 15% ... you screwed up.

There definitely aren't easy answers to these kinds of problems but there are steps that should be taken along the way to prevent them. Getting to the end and then addressing any and all performance issues is a recipe for disaster.

You don't want to be making major architectural changes at this point in the process. You want to be dealing with hiccups. Throwing hardware at the problem and "optimization" only go so far.