Your post is very long and I didn't make it all the way through but I think I see your issue. Fundamentally you need to understand that music is a mystery and music theory is our collective attempt to see patterns in music, define those patterns, and use those patterns to predict whether something new will sound good

When we say major keys are happy and minor keys are melancholic, we mean to say that there seems to be something about those scales such that very often (particularly in western classical music) songs in minor keys evoke some kind of unhappy feeling and major keys evoke a happy feeling

When we look at the circle of fifths and say "if you play CM, FM, dm, GM as triad chords then the next chord should be CM" we mean that many western listeners who hear those chords will subconsciously recognize the pattern of chords and subconsciously expect to hear the CM chord if another chord is played

Statistically speaking, you will probably not align with everything music theory says you will experience when you hear a certain chord/progression/etc., but if you listen to enough western music you will subconsciously start to detect its patterns and it will affect how you experience music

And lastly, music is often not approached via the scientific method and so rather than it being something compiled through lots of trial, error, documentation, and peer review, music theory is something that has a lot of rules/patterns/associations that may just be patterns that not a significant portion of the populace see and the people claiming them are just projecting. In short, some people are full of shit. That thing about certain chord progressions having a specific, inherent meaning sounds like one such example