Leo, there are times when you can have your cake and eat it.
I agree with writing an anger journal but what you have advised is also wise. If someone is very angry and writes stuff like "I am going to kill that bastard" then even though he or she has no intention of doing anything like that, they may get bitten if by some unusual circumstance the journal gets read by others. .
One way you can write an anger journal is to write it as a novel. And it is also important that you not only write about the feelings of the main character (who is of course the author of the journal) and their thoughts but also those around them, whom the main character feels annoyed or angry with and any events that have taken place, whether they appear related or not.
You will find, on looking back over your work that those people you feel angry with are often (not always) the offenders. The methods that are used are devious and cunning. In causing a person repeated anger or anger that appears more than what a particular incident warrants, is often part of a foul game that toxic people play.
A concealed threat is used, which means the person becomes energized but doesn't realize it is fear. At the same time an idea is presented, either mentally by a related party or verbally or an issue of injustice or violation is done. The person reacts angrily but as their body is charged up they feel more angry than they would normally be over the matter.
I have made a series of 5 videos here:https://www.youtube.com/watch?v=7nxUl19yZU0&list=PL0vGp6lNGae1V9U4CmtAI0qAuxWZ2DzEg to explain how this is done. It is not a simple matter.
And for the benefits you gain...
At least you have a journal and can, over time figure out what is going on and who might be a false friend. The knowledge you gain can help you stand against the enemy and rob them of the pleasure they get from your suffering. And there are very good ways of counter attacking them, which are wholly mental.The battle is fought and won in the mind. Psychic warfare. Have a look at the last illustration on this page here:https://kyrani99.wordpress.com/2012/03/15/solutions-what-you-can-do-to-prevent-heart-problems/
And you get to do some creative writing, which being a human story, others will find interesting. So you may in the end conquer your anger, deny any toxics their narcissistic supply and publish your story as a book and make money from it.