I suspect it is due to how a letter grade can represent a range of potential values, which could also be subjective to a grading scale set by instructors. An "A" for one instructor might represent an "A-" or "B+" for someone else. As such, Canvas defaults to entering points. Points can be more easily converted into another method such as a percentage or letter grade, and play nicer when communicating with an external SIS.
Setting up your grades to show something other than points should not be tough. Within the assignment itself, you can adjust a setting for how to display points: https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-add-or-edit-details-in-an-assignment/ta...
This does still involve entering in points earned on an assignment, but will display a letter grade as an output. You could also set up a course grading scheme so that if you choose letter grade, you can have a defined scheme that determines what letter to show as a grade: https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-add-a-grading-scheme-in-a-course/ta-p/1...
https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-add-a-grading-scheme-to-an-assignment/t...
When you say they do not automatically show in their transcripts, are you referring to the Grades page on Canvas or an external system? They should show up immediately on the Grades page, if you have it set up to automatically post (Go to Grades page and select the gear icon in the top right, then Grade Posting Policy). If set up for Manual, you have to initiate posting them for students to see, but once you do that, it is almost immediate on their end.
If you are using an external system for transcripts, then yes, it likely is not immediate. If that system has the ability to sync grades, you can set up Nightly Sync to sync grades every night: https://community.canvaslms.com/t5/Infinite-Campus-and-Canvas/How-do-I-automate-course-grade-sync-fr... Otherwise you have to manually sync from the Grades page.
As for the user-unfriendly, please consider making suggestions on the Ideas page. It is currently going through an upgrade, but Canvas does listen to feedback. This is a subjective opinion, but one you likely are not alone in feeling. Making suggestions is how they find new methods to implement. Is there a particular aspect you feel is unfriendly (beyond what you have already mentioned)? I have see coworkers also annoyed with it at first, but maybe myself or others could help identify what is frustrating you and a path to reduce that frustration.
