There is one huge thing that is being missed here by both of you. The Google Insight grades on server response time. Server response time has no bearing on if a site loads 1 css file or 30 css files. It has not bearing on how many js files are loaded and if the parsing of them is deferred or not. If you follow all of the suggestions that pingdom gives you to the T, it will not affect your server response time one bit.
The only way to affect your server response time is going to be to reduce the processing time of your site. Not the loading time in the browser. To reduce your server response time you are going to have to explore server caching, mysql optimization, and things such as that.
This might help to read as well.
https://support.google.com/analytics/answer/2383341?hl=en
http://www.blogaid.net/server-response-time-vs-page-load-time-for-google-crawl