A better analogy might be those smaller cola brands with higher caffeine levels. I don't know if you have these in the US; in Germany, there are a lot of them (e.g. Fritz Kola, Afri Cola, Club Mate Cola).

On the outside, it looks similar to Coke/Pepsi (still cola), but it has a vastly different and smaller audience (people who need caffeine, but despise the sugariness of energy drinks). But they stay in their niche, because any attempt to replicate Coke/Pepsi would get them crushed between those two.