Ahhh. SOS...I still like that better...
Whereas it does take a lot out of the ref core and may put some fans to sleep. It is a testament of player athleticism and ball control over the endurance of the match.
The rotation design of volleyball positions brings out an element that differs from other sports in that players strengths and weaknesses are brought out, especially that crucial skill of passing/digging. That which the libero has changed that one aspect of the game and changed the strategem of the sport with the player replacement instead of taking a substitution.
RPS takes the best server and caps their opportunity. If you play to 25 points, unless the best server begins the match, basically they'll have at the max of 5 chances, if there were to be an overturn in each point. While with the old SOS, there still wouldn't be any score.