I usually reframe from writing this type of post because it typically raises more arguments verses discussions, but here I go.
Science has stated that they can not determine what actually causes muscle growth, mechanical stress (heavy lifting) or metabolic stress (higher rep range) but they can determine that progression is the mother load of muscle gain, regardless of rep range.
With that being said, you have to progress and a person is more likely to progress, if they work in all rep ranges, being, hypertrophy, strength and power, or know as 8-12, 5-6 and 1-3 respectively. The discussion on sarcoplasmic hypertrophy, as I know it, comes from working in a higher rep range, to where the muscle depletes glycogen and super compensates by bringing in more glycogen, thus attracting more fluid (usually at a rate of 2.7-3 to 1 ratio) and this is what we consider sarcoplasmic hypertrophy.
Both have been proven to work together synergistically on building lasting muscle. If a person works solely for the pump (higher rep range exclusively) he will lose a great deal of that, over a matter of a few weeks of not lifting, when the water retention leaves.
If a person works in lower rep ranges, it is harder to get a pump (less time under tension and depleting glycogen) but they will still grow but it will take longer to show but will not dissipate as quickly (atrophy) because there wasn't as much water retention in the muscle, so less shrinkage.
Remember, this is what I've learned, through some schooling and an obsession to read about the subject. I'm in no way saying that I'm 100% correct and I'm always trying to learn more, that's why I'm here.