How about if we train each bodypart once per week AND use all 3 rep ranges? Best of both worlds?
I always train muscles more than once every 7 days so don't know from experience but if I was to train them once a week I would be using all 3 rep ranges, starting from heaviest to lightest to get the best of both worlds, as you put it.
In the big picture, the ranges are just a guide for me to dictate weight and I do not really over analyse it. If I am going for 5-7 and I get 9 I raise the weight, if I get 4 I lower the weight etc..
In the long term as long as my weights are going up within that range it wont matter when that weight I am lifting doubles if I am lifting it for 5 reps or 7 reps.