I would disregard most of the advice offered. It's good to reduce adverbs and passive phrasing, but I see little use in dumbing down sentence structure and word cjoice.

It depends on the purpose of the writing. I intentionally dumb down all of my business correspondence to make it direct and easily digestible. If it doesn't get 9th grade or below after a Flesch-Kincaid scan I've got some editing to do. The last thing I want is for someone to have to reread a sentence to understand it.

I wouldn't run a novel or short story through it though.

For shits and giggles.

Before - https://docs.google.com/document/d/1EvLGOaSuBwo89RKZIfoD0R-KdOHx7eY4rRjbKtVZVxY/edit?usp=sharing
After - https://docs.google.com/document/d/1Yxjqpd13IugDj3UhoaaJcbMMrq-tt7tB_Gh-uS2jb14/edit?usp=sharing

I primarily write advertising copy.
Dumbing down is a pre-req.

Good points. I was thinking of fiction. That's where my mind ranges.