Well technically none of them are running simultaneously unless they're on different cores. Even if you have many processes active, most of them are sleeping most of the time, which is why you can have 100+ processes active and still have CPU usage under 10%. The OS scheduler will service all of them and still have time to sleep for 9 times as long as it took to service them before it has to do it all again. Word spends most of it's time waiting for a keystroke, safari spends most of it's time waiting for you to request the next site or scroll the page. This is all time the processor can be asleep and saving battery.
If you're exporting video from final cut pro, none of this applies.
edit: not saying you're wrong. I'm just speculating and I'll be interested when there are actual numbers released for eg. Core i5-7500U vs Core i5-8250U