I think there's a wide difference between actual effective communication and what people call effective communication. The former is characterized by getting to the heart of the problem and finding a resolution quickly while the latter is usually characterized by following social conventions to show deference to titles and individuals. I'm a bit biased here but I find autistic people tend to be competent at actual effective by saying the quiet part loud or addressing the elephant in the room even if people find it a little off-putting. That's not to say that's a good thing in every situation

This is assuming that there is no "selling" required. In a lot of cases some selling is required and then just being some sort of blunt isn't necessarily helpful.

I agree, but it's also easy to build up a clique along some lines, be they socioeconomic, or what politeness rules we decide are important, or whatever else, and those can easily exclude people who want to be kind, but also just tell the truth and make progress.

I think it's wise to be on the lookout for people and groups employing strategies, conscious or otherwise, that de facto degrade simple communication.

That reality was created by managers that only care about themselves and that see any capable individual as a threat. It doesn't have to be this way.