The marketing funnel offers a good basic model, but marketers need to be aware of how technology has altered the buyer’s journey. Many buyers do their own research online, comparing features and benefits of competitive products, rather than relying on a company's traditional marketing activities to guide them through the funnel stages. This means buyers enter the funnel at a point where they are more prepared to make a sale. It also means companies need to get information online, such as an up-to-date website, product content and purchase reviews.
As a software engineer myself, I can tell you that building funnels from an application standpoint takes massive amounts of work. There's a great deal of coding and integration that's required here. From email systems to landing page implementations to credit card processing APIs, and everything in between, so many platforms need to "talk," that it takes the bar too high for the average marketer. 
Any claim that AMP ensures a certain level of performance depends both on how forgiving you are of the extremes, and on what your definition of “performant” is. If you were to try and build your entire site using AMP, you should be aware that while it’s not likely to end up too bloated, it’s also not going to end up blowing anyone’s mind for its speed straight of the box. It’s still going to require some work.
Page speed is often confused with "site speed," which is actually the page speed for a sample of page views on a site. Page speed can be described in either "page load time" (the time it takes to fully display the content on a specific page) or "time to first byte" (how long it takes for your browser to receive the first byte of information from the web server).
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