I made a solution that is entirely contained in a WordPress plugin and doesn't rely on Xdebug xhprof or any PHP extension. Please give the WordPress Hook Profiler Plugin a try. There's still room for improvement but the core functionality is there:

Show which plugins take the most execution time:

Show which individual hooks of the plugins take the most time:

It's implemented by running through every hook and replacing them with a new callback that wraps the original call back to record the time it takes to execute. Also a mu-plugin adds some hooks to time the loading of the plugin files themselves. All-in-all it will show you that, that page builder you using is probably what's slowing everything down.