I note we subtly slid at least partially from how powerful fighters were vs wizards were to which one would win in a 1:1 PvP, which is interesting in its own right, but not really the same thing. Most of playing the game wasn't 1:1 PvP, it was both classes being played together (in groups alongside the rest of the classes) with various expectations like fighter-types provide interference to try to help the magic users get their spells off and magic users casting spells which support their side's fighters. Likewise, the general measure people would have used for how 'powerful' each on was was... well, there would be a lot of variation, but I suspect much of the time it was how much you felt playing as one or the other contributed towards overall party success.
Regarding RAW, Core, Optional, and Official (as I see it): --
Official is whatever the publisher declares it to be (usually distinguishing their material and whatever outside material they endorse from any other material).
Core, as we in the (TTRPG and computer) gaming community use it isn't so far as I know a technical term. Certainly outside the community a game's 'core rules' probably means something like 'key elements' or 'most often used rules'. Within the community, it is generally used as the main or original components, as distinguished from expansion material. Its primary usefulness is in understanding that many-to-most people who have played game _______ may or may not have played, or even seen/heard of any given piece of expansion material (and yet still recognizably played the game).
Optional is, well, optional. Technically all of the game is optional, but this is officially declared to be a variation to the default that you can instead do and still officially be playing the game as opposed to a homebrew game based on the official game. Notably, optional rules are Official, Core, and/or RAW if they meet the other criteria of those categories.
RAW is whatever is in the printed material (general convention: actual declared and published errata can overwrite what was actually printed in the books). If there are multiple versions of the whole of the rules (such as Core and Core with supplements) there are also multiple versions of RAW. If a ruleset contains multiple statements on a subject, they are both RAW (even if they contradict, there is nothing stopping RAW to be paradoxical). RAW also only covers those play facets it actively speaks to. Anything outside that purview is moot and variations in play pattern which do not touch upon those facets do not impact whether a game is being played RAW or not. So, for instance:--
Well this is one of the methods in the DMG, roll I think 12 sets of characters using 3d6, then pick one. It is method 3 or 4 above and would still mean 1 in 20 parties or so had a magic-user with an 18.
Now if you rolled hundreds and hundreds of characters, or if you used one of the other methods and rolled multiplee characters that wasn't RAW.
Is overinterpreting what RAW adjudicates. I'm only looking at the character creation sections of 1E DMG, PHB, and UA, so I might be missing something. However, so far as I see, the rules do not comment on how many sets of characters someone should roll (outside of method IV dictating roll twelve and pick one as a method for a single instance of character-stat determination). It is silent on the issue. If a group allows people to repeat the character creation process multiple times until they find one that is satisfactory to them, RAW does not come down one way or the other on it. Nor, for that matter, on people abandoning sub-par stated characters, or simply not trying their hardest to keep them alive. Simply put, RAW dictates (so well as it carries weight) rules for the procedural generation of character stats. It says precious little about what distribution of stats will be typical in a PC party, either at a time or over a significant period of time.
All that of course notwithstanding whether RAW is meaningful. Most 1E and other TSR-era gamers I've met steadfastly acknowledge that they never tried to play 100% RAW. Some others indicate (believably, I should add) that they followed a given subsection of the rules by-the-book consistently. That of course acknowledges that they feel not all of RAW is necessarily important, so it leaves open why that subset somehow is. Of the small remainder that say they played purely RAW (leaving aside that there are different RAWs depending on what books you include), most (probably obviously) I have insufficient information to draw firm conclusions. However, of those I do, I've yet to find any that weren't forgetting or overlooking one or more exceptions.
Regardless, let's say there is a group that follows every RAW rules as written in the books (whichever self-defined set of books included) completely and to the letter. What does that mean to anyone else? This is insufficient to me for any arguments about how things were, how it should have been/should be, or how the games of yesteryear should be seen in retrospect. Not that it means nothing, simply that additional case needs to be made.
As often as not we were using premade characters, and among those magic-users were generally weak.
I believe that to reasonably be the case immaterial of stat distribution. Magic Users can be weak, just as fighters. It all depends on how the game was played (playstyle, not rules used). What situations come up, what treasures are rolled (magic items and spells found), how people perform with regards to caution and strategy. Everyone was fragile enough to die to a situation set up to play to their weaknesses, that they weren't prepared for, or that they didn't understand. Don't play with front-line screening (and wait until you have some tricks up your sleeves before you forge into the wilderness), bunch up when you run into breath-weapon enemies, be the front-line if the DM loves gimmick monsters like level-drainers, or heck just be the first character to encounter 'do this or you're dead' puzzle monsters like green slime and things go wildly differently for different members of the party. Your experience can differ from their experience completely without differences in stat distribution or what RAW rules are enforced or not.
Ah, I had the opposite experience, in my group, every book was basically kosher, though only the main DM used Comeliness (and continued to do so into 2e). The mindset was "if TSR printed it, it must be ok".
Everyone yelled at me when I banned Cavalier subclass Paladins, but I stand by that decision, lol.
Everyone I know who played BitD had a different amount of rules material, be it core, core+UA and similar supplements, or all the way up to every Dragon magazine and every campaign setting book (and possibly even books which technically belonged in the oD&D/basic-classic line). Likewise, everyone sees their experience as normal. It's worth pointing out that plenty of people played years of campaigns of AD&D in the eight years between when the line started and when UA was published. Yet they were all AD&D. I think the diversity of play experiences is one of the charming things about the edition. However, it certainly does make it hard to discuss how the game went bitd, since it definitely went very differently for different groups.