Grammar privilege feels 90% understanding the audience and timing vs something like 10% power dynamics. As with most things where there can be a power imbalance, that does not mean those with power (e.g. managers) should not help set expectations on an even field with each of their employees anyways. Nor does it mean the other 10% of cases don't exist, just "don't ignore that 90% of this is probably one being too worried about sounding professional in every possible scenario".

Before going into the workforce, we're usually taught professionals are expected to communicate like professionals 100% of the time. It's just the safer bet to make as it's simply a lot harder (though certainly not impossible) to foul things up in a professional situation by having good grammar and well written emails than vice versa.

That said, it seems like most people I've ever actually worked with (on any level) do not like communicating 100% professionally the majority of the time (especially in small groups/directly) and may actually consider THAT disrespectful. Some from practicality ("don't waste so much time on an email we could have talked through casually in a minute" etc), some for just having different social expectations ("We've worked together for 3 years, why are you sounding like a door-to-door salesman about to make a pitch to me instead of just saying you had a thought" etc), or a laundry list of other reasons. Telling when and how much professionalism is expected is just something you have to learn to read the individual/crowd for, but it's probably a positive signal a lot less often than the author assumes it usually is.