I understand Exec Sum is the sum of all methods within PP, as explained here
However, in this captured PP the exec time is infact the summary of entries that are not methods:
Web request + web request + doFilter()
doFilter is infact a method, but the other two are simply header nodes in the PP tree.
Is this how the Exec Sum should work? Bringing into account every node of the PP tree even if it is a "title" ?
Short answer yes, think of it more as it moves through your web server and how it flows through different tiers, the communication takes time.
Longer answer: The Exec Total you have highlighted is showing you how much time is being spent with the purepath. So for your request to finish the web server takes 3360.69ms to complete this particular purepath. As the request move through the different areas we look at how much time is being spent on that tier so at your servlet level the servlet "works for) 3358.25 ms with .02 ms spent on your first sensor. So in summary the purepath tree will show exec time of everything making up that tree.