The SPL Handbook says the SPL appoints them and the Scoutmaster approves of them is this true?
I believe you will find the Scoutmaster Handbook, the Senior Patrol Handbook and the Leader Specific Training to say that the SPL selects ALL troop junior leader positions with the advice of the SM, and the only one it says requires
approval of the SM is the position of Junior Assistant Scoutmaster.
This is not to say that many units don't do it differently, only that the leadership method designed and supported by the BSA is to let the SPL make the decision as to who his cabinet will be. Much the same way that a President chooses his own cabinet. As Baden-Powell said..Train them, TRUST them, let THEM lead".
Certainly the SM is better equipped to make these decisions, and the troop might very well operate better if the SM did make these decisions. The question which is left to each SM to decide is "what do you want?".
Is the goal of the scouting methods to have a smooth running troop, or is it to develop the boys abilities to make ethical decisions? Certainly allowing the SPL to make these decisions will bring a unit closer to the goals of scouting..if that is what the unit wants.