I don't have time to respond to this long post of yours right now but would like to get to it later. Just noting that.
In B/X (and its clone OSE) three races for adventurers ARE classes. So when I see a class which has a bunch of abilities which are a good match for the fictional concept of the Ranger, it doesn't matter what kind of class that is. I can "re-skin" it as being a Ranger without changing the mechanics at all and thereby enhance my game by enabling an additional character archetype without even needing to write new rules.
Yes, very much against some of AD&D's worst and most wrong-headed rules. Minimum ability score limitations in OD&D and AD&D were SORT OF fun in that they made for a kind of gambling sub-game in character creation, where you had to get lucky to roll well enough to play certain classes. That can be enjoyable, at least assuming you play enough D&D that you have lots of opportunities to roll up characters. But that is not an assumption which applies to most people, nowadays or even forty years ago.
The idea that it's more balanced is absurd. Silly. Deeply and profoundly incorrect. Gating the Paladin or Ranger classes (for example) behind high ability scores is the
opposite of balanced. It is a "the rich get richer" mechanic, meaning characters who are ALREADY advantaged by having higher ability scores than most get EVEN MORE BENEFITS by qualifying for classes with more special abilities.
Removal of racial and alignment restrictions on character classes is a matter of taste. I enjoy both concepts of Paladins- the shining hero archetype AND the more flexible champions of various alignments. But the latter is not a new concept. WotC didn't introduce it even 25 years ago. Dragon Magazine introduced the Anti-Paladin class in issue 39, July 1980. And there was a very popular "A Plethora of Paladins" article in issue 106 which introduced rules for Paladins of the other 7 alignments. There were both in the 80s, for AD&D.
Racial or alignment restrictions on classes can suit particular campaigns. But removing them from the core rules 25 years ago was really just continuing a trend of enabling more player choice and flexibility with character concepts and classes which goes all the way back to the beginning. As we already discussed with how the Greyhawk supplement in 1975 added a whole new class and a bunch more options for demihumans. And the AD&D Players Handbook added even more in 1978. And Unearthed Arcana even more in 1985.