Well, lagging left should be beneficial to more drivers, as most drivers continue on straight then make a left turn at any given intersection. The main issue for lagging left (that’s fully protected) I think would be for queuing left turn vehicles potentially ending up beyond the left turn bay into the regular lanes, a leading FPLT allows the left turn bay to clear before the main green starts allowing the left turn bay to be filled again.
As I understand, the only other time you can squeeze a green in for a transit ROW would be between the barriers, that is when the intersection is under red clearance (also known as “all red”, when every light in the intersection is red)