I am at "large tech co"
> 1. You often have to write design docs to communicate what you are making and gather feedback. These documents if badly written won't be as well received.
In my company this is entirely up to the culture of the org. Some parts of the company will require it. Other parts treat it as a formality (i.e. few will read it). And other parts don't require it at all.
> At many companies, you have a million things to work on, so in a way, you get to choose who you work with at some level. If someone communicates badly to the point of annoyance, it will take something special for you to decide to work with them or not.
The key phrase is "to the point of annoyance". If most people are poor writers, they are not annoyed at the fact that their peers are poor writers. Even worse, being a good writer is not an advantage.
If your culture doesn't value it, then it is not of value.
> 3. To convince execs and managers to approve your project ideas, you often have to write a document explaining your idea. If it's badly written, the exec isn't going to be as interested in it.
I addressed this in my comment and won't repeat what I've said.
> 4. To get fame as an engineer, you often should write compelling blog articles. Badly written blogs tend not to be read.
I suspect this is reflective of the SW point of view. My company is an engineering one. It is a giant, and is usually the top company in its discipline. I've worked with engineers who are likely the best in their discipline globally, and often way ahead of academia.
Not one of them has a blog - internal or external.[1] Very senior leaders tend to have them, and they usually are not technical, but corporate speak.
Keep in mind: Most of the engineering world is very different from your typical SW company.
> 6. Promotion is often done by a committee of people who don't know your work, and all they are going to do is review what you wrote. And promo is often based on leadership of projects. And how do you become the leader of projects? You write compelling documents.
In your whole comment, this most reflects how unreflective your perspective is in the engineering (and even SW) world. Yes, I do know some companies that do promotions via a committee of people who don't know your work (Google, etc). For the rest of the tech world, this is rare. People get promoted because they have a manger who will root for them in front of the committee. The committee is typically the next level manager, and he/she likely is aware of your work. There's no "promotion packet" that one writes. There's the annual review (under 2 pages), and the committee only scrutinizes it if your manager is pushing for a good bonus or promotion. And as long as its readable, it's good enough. Of course, this means that spelling errors and poor grammar are OK.
When you want to get to a really senior role (usually takes 15+ years in the company - less than 1% of employees reach that level), only then does a wider committee get involved and will scrutinize your work. Do you have patents? Do you have external publications? And this is only for a technical role. You're not subjected to this scrutiny to get into senior management. Which is why surprise, surprise, we have a larger number of senior managers than senior engineers.
> And how do you become the leader of projects? You write compelling documents.
Oh heck no. You get an idea and pitch it verbally to management.
Trust me - a very consistent feedback I've gotten from management at work is "You write too much. No one will read what you wrote" - almost always delivered after I write an email that has 4+ paragraphs. I'm not claiming I'm a great writer, but they don't give up because they find my writing hard to read. They give up after seeing that the email doesn't fit on their screen. If I have a "tldr" they'll read that and talk to me in person (only a tiny minority will read the actual email).
Culture is king. Writing well will serve your career only if you are in a company that values it. Let's not pretend that writing well will take you places in organizations that don't value it.
[1] I should say that they do not openly have a blog. Some may have ones they don't publicize. Having a technical blog you spend a lot of time on would not be viewed positively, and the more senior you are, the more people will be concerned you'll leak IP. The company is pointlessly secretive and senior management doesn't want to allocate resources to vet your blog's content for IP violations.