Obviously its your opinion so I wont argue to much but I agree that Voss would improve more
Because Ratten is already better than him
Yeh Ratten has better runs on the board as a tactical coach - but that was mostly his midfield work, and as I said, we have George Stone.
Don't underestimate Voss' ability though. He had a terrible list (and some poor recruiting decisions that set him back) - and his sacking was not for poor performance (just like Ratten incidentally). The guy has worked with some excellent coaches, and let's not forget he was a 3 x premiership captain and one of the best players of all time - and he's an excellent analyst and communicator in the media so he knows his way around the game.
But it's probably Voss' relationship and leadership ability that sets them apart mostly in my opinion.