You are right. It performs the steps from left to right and doesn’t actually do anything truly at the same time. And, if it gets stuck on one side, it is still stuck. This also means that both sides will not end at the same time so you need to use a loop that ends when the longer side ends, depending on what you need it for.
One thing you could try however, is use an Invoke Workflow in the parallel. I have not played with this enough but have heard it works better that way.