Not sure where you're getting these "heavy and bulky" stock saddles. Stock saddle's cantle and pommel may be slightly higher on some of the modern models (like mine), poleys are smaller then the knee rolls. Without the stirrups it's under 19 lbs. While it's not "light" compared to a good endurance saddle it's certainly not what would be called "heavy". Even the stripped down McClellan weighed 17 lbs.
Less tree will give you less weight, but it also concentrates more pressure on the horse's back.
This is my 16.5" seat stock saddle. No bulkier than an "English" saddle, but more comfortable.