Games should be 5 battle rounds, not 2. Therefore on average it should not be just one of the players who get a double turn in a given game.
Also it is a “priority roll”. Not a “double turn”. The point of it is to pick whether going first or second benefits you in a given round (consider placement, endless spells, victory points, benefits of a double next turn etc). In your games you should be planning when you want your double turn to occur. When it is better to give your opponent a double if you win priority. Etc. It adds a tactical component to the game to consider. For example when I play Idoneth I want the double turn from flood tide into high tide (whether that’s 1-2 or 2-3). If, for example, I want it 2-3 then I will work to give my opponent priority on turn 2 and play turn 1 expecting to be double turned (assuming I went first)
it also adds a neat mechanic for endless spells. A few of them on the field and it adds more tactical considerations. Overall it makes it a more interesting game.