Here's my take on it:
Writing is easy. Good writing is hard.
Anyone can sit down and come up with a plot, characters, and write a hundred pages about it, but the difference is in how much energy and passion the writer focuses on the work. I used to think that writing was easy, and that was because ideas came to me naturally, but like when a person starts drawing, they're always going to improve. There is always room for growth! I've been dreaming about writing my whole life, actually writing for seventeen years, and seriously writing for the last five.
Hell, I look back on things I wrote barely a year ago, and they're just bad, bad, bad.
General rule of thumb: any book that was ever enjoyed had to be conceived, written, looked over, edited, perfected. Then the length cut in half and the process repeated.
There are many little nuances that go into writing, like styles of point of view, tense, if the author switches between characters or not, foreshadowing, symbolism, long nights staring at thesauruses, agonizing over if the alliteration should be put in or avoided, making sure you don't use the same word twice in the same paragraph, running out of words and thinking of a completely new way to describe the color of your characters eyes besides the word "blue", etc, etc, etc.
If you care about what you're writing, then writing is never easy.
Mental aspects aside, it takes quite a toll, physically, as well! As a writer, myself, I probably sit at a desk and work for about five hours a day. My back hurts from not sitting in my chair properly, my neck hurts from looking between the keyboard and the monitor, I live a sedentary lifestyle because of my passion and have to make time to move around lest I risk blood clots.
As for hiring different people to write different characters! It's only a waste of resources if the writer is bad lmao
For example, I'm writing a fanfic with my friend at the moment, and while we are writing it word by word and line by line together, when it comes to the interactions of the characters, my personal writing style better fits the voice of one character, and my friend's is suited to the other. Together it makes for a more organic, authentic experience.
ALSO speed NEVER equals quality!
You can be speedy and write well, but it is r a r e
But that's my opinion!