Parallelizing is plain simple "await Promise.all([first, second])"
Problem is doing some serious synchronization like n at a time or similar. Those things are better of with callbacks
await first
await second
await parallel(first, two)
I understand your point that not knowing how promises work can lead to not optimizing them, but going from one to the second can easily done on another iteration. On the other hand, not being capable with callbacks can easily lead to (callback) hell, then you need to first fix the mess, then optimize.