Very simple, really...
True .. but only once one gets one's head around the techniques.
When playing with trimsheets one sees a range of designs ranging from very bad through to very good (and the latter, generally, are presented fairly simply).
I can recall a task to design a GII trimsheet many years ago now (about 30 years ago, as I recall). That little exercise took me some weeks to figure out a way to present a tidy double envelope to account for trimming at ZFW but still needing to determine CG at takeoff (as I recall that was the main problem). Once I figured out a way to do it, it was all very simple .. but I had a few worrying moments along the way trying to make something work. Another very experienced engineer had given up and suggested that it just couldn't be done ..