So their order for 150 777x would fall into the same category?
Ummmm, emphatically, NO. The 777 has orders form several dozen different customers. That's a huge customer base. The 777X is still in development and there is every indication that it will have as many different customers as the 777. But yes, Emirates will be a huge customer for the 777X just as they are a huge customer for the 777. They've ordered 152 777-300ERs, but that did not make the 777 a niche product.
By the same token some airlines have bought literally several hundreds of 737s and a number even have all 737 fleets. The does not make the 737 a niche product by any stretch of the imagination.