Empathy has it's place
There are two ways of writing in general; one with lots of emotion and invoking of feelings, one without those qualities.
Emotions
So emotions work great in fiction and where you want to spin a yarn, tell a story, pass along an anecdote or otherwise want to convey some emotional state to another party. This works great when regaling the grand tale of when you first fixed that bug nobody else could fix. That is a tale that works great with emotion.
If you take all the emotion out of it you end up with a one-liner.
I realised what the issue was, and applied the fix accordingly.
This is not how you felt at the time, how others perceived you, what cascading effect this had on your career choices, life choices and otherwise effected you on a deep personal level.
Facts
This is not be confused with factoids, which are facts presented as being true whilst being based on something false or because it appeared in print.
So sometimes you do not want to have emotions in the text. Like when explaining complex mathematics, or instruction manual for fighter pilots, or maybe an escalation e-mail within the company.
Wording
The tone of the piece of text is also determined by the wording, or vocabulary being used. If it needs to be lively then go for the buzzwords, making up stuff as you go to further enhance it. If it needs to convey some message correctly and streamline the discussion to what you want to talk about then tone it down, use more academic kind of wording and be more explicit and unambiguous about what you are saying. In the latter it cannot be misconstrued in some way.
Take the emotion out of it
So in order to write a good escalation e-mail, or any piece of text, what my advice is, is the following. You write your text in a text editor of choice. As far away from the e-mail program as possible for fear of accidentally sending it. You write everything down from an emotional standpoint. At the end at which point you reread your text you think of the question:
What is the goal of this e-mail?
In other words, what do you want to gain? The message is not created by the one sending, but the one receiving.
This means to adjust the wordings in such a way that only the bare neutral essentials are left behind and on that basis the further discussion can take place. This means to take the emotion out of it. Take every sentence or paragraph and turn it into facts and neutral wordings. Example:
Then person A said .....
Turn it into
As was stated in the conversation as such ...
This makes it into the fact it was uttered what is important, and to some extent what was uttered but not so much who uttered it. This process can be repeated on the same day, but also the next day. Sometimes it helps to have a cooling off period in between to make sure you can more easily take the emotion out.
Apply some structure to your e-mail. Group content together, where possible use some small headers to delineate what the section is about to also make it easier for responding parties to refer to sections.
This also is linked to going nuclear.