I was curious these days on why it takes seconds to load the page without cache.
So I use xdebug profiler and qcachegrind to profile performance issue of flarum.
With cache disabled, I find that Less compiler is the performance killer(more than 60% of total time). My suggestion is make a command to compile less and watch less changes but not compile when noticing less been changed when processing requests.
It can enhance extension development experience a lot when setting debug config to true.
And I also profile Flarum with debug to false, so that less is not compiled any more after the first loading. I find that symfony/yaml library cost the most time. So I wonder if the code calling symfony yaml can use php yaml extension in priority.