How much experience writing letters to the editor have you and that suggests that such letters are effective?
Traditionally much of a newsrag's governance is set by the editorial board that may be made up of pretty much whoever the publisher wants. They set the editorial policy quite according to their whims. The reporters then must then toe the line and may not even be on the board.
If your Letter to the Editor, however well researched and written, doesn't please the reporter assigned to the LtE column then it will not be published. If it is published then the reporter may edit your work, even into nonsense. If one of your letters is published then the next one may violate a fair access policy and be spiked for frequency - too many letters from one subscriber would never do!
One of my proudest moments came when the Letters Editor at the Charleston Posted & Currying announced that she found me, unmet, "personally offensive". I never had a letter again published by the P&C in spite of being acquainted with many of the board. Barbara McDowell has since retired and the LtE have not improved. I read them every day.
I also read the Door County Advocate weekly and weakly. What a POS.