I do tend to cook like this, but that's because I'm an inexperienced cook :-) I don't trust my ability to complete a prep task in the bounded amount of time you have once you've actually started cooking, so unless the time available is clearly long and the prep task trivial I tend to do most to all of the prep in advance. You're absolutely right that it takes longer in wall clock time but I find it less stressful, and that's valuable to me.