At face value, this statement is obviously true-- a talented junior is very likely to be better than a comparably talented freshman.
The X factor is that basketball is a team sport and does the team put a player in positions to be successful in performing her role (and how is that role defined). If KJH is the big coaching upgrade LV fans are hoping for, then Horston will be better prepared and situated in a more effective dynamic offense and surrounded by players who have upped their respective games. So, I think it is possible that Horston could, in effect, put up better numbers than Evina did this season, which is the most direct comparison. Indeed, if Evina was on the team, I would expect that her numbers, next season would be better than Horston as the starting PG. But in the world we have, the relevant comparison is can Horston be better, or as good, as sophomore Westbrook.