Personally, that sounds like a really odd complaint to make. After all, running promises in parallel should be just a matter of using a simple library function

Personally, that sounds like a really odd complaint to make. After all, running promises in parallel should be just a matter of using a simple library function that you can very easily code yourself if its not already provided. I tend to find that the biggest problem with promise libraries is writing code with lots of jumps and more advanced control flow. If you are using an explicit continuation-based approach then doing a jump (for a loop or for breaking out early) is just a matter of calling the appropriate continuation. On the other hand, promises naturally tend to prefer the sort of code where there is only a single return statement at the end (unless you abuse the error handling system but there are all sort of problems if you do that)