You most certainly did not make it clear that you were only considering examples of courses where there were only two equally weighted assessment items. It is just too unusual.
OTOH it is not so unusual for a course to have a final exam that is worth up to 50% of the course total. Of course, if you are going to give that much weight to a final exam then you can't complain that it has a disproportionate influence on a student's final marks. The solution is to not give so much weight to just one assessment item.
Is the concept of "ordinal data" too complicated for you to grasp? If the "points" are not being added together then if makes no difference what numerical value you attach to each grade provided that A > B > C > D > F. All such scoring systems are equally valid and a fail is a fail is a fail.
Let me try this and wonder if you were teaching high school: in all of the systems I worked in and all that I have discussed with other non-local teachers, the grades, their values and (where the computer is god) etc.are weighted (tests, quizzes, homework, projects - being different weights with tests usually the heaviest weight) and those are required of all teachers of the subject(s) to follow.
The systems tend to have requirements also re: make-up work, attendance effects and related matters. While it may not be to our or your liking, them are be the rules if one likes to stay in the education game. College tends some differently, so, if you are teaching college these rules may well not apply, but in public school they very much do. If this is insufficient please let me know which points you take umbrage at or think we/I are/am making up to cause you distress. I do assure you that nothing I have posted is untrue in the systems I worked in more recently (now retired)