This tangentially brings up another big difference between 1e-era play and today: party size.
In 1e, parties of 8 or 10 characters were common; and a lower-level character could kinda hide among the numbers until it got its feet under it.
In 5e, the party is expected to be only 4 or 5 strong, meaning any weakness is going to quickly become apparent. That, and the whole WotC thing where the encounters are expected to match the party level (or vary by a specified amount). Each WotC edition has a different name for the system it uses but the principle is the same, and I see it as a bug rather than a feature as it tends to force the game to be played within some fairly tight parameters rather than the TSR-era idea of more free-form variability.
To explain: 0e-1e-2e didn't care if your party was 3 characters, or 8, or 12 plus a marching band. The adventures gave a suggested level range (which may or may not have been adhered to by any given table!) and that's about it: the DM had to vary things from there if needed. In the WotC editions where it's almost dictated that parties shall be 4 characters, no more no less (5 is allowed in 5e) the same holds true, only that DM-varying process has been made far more math-heavy and complex (says he, recalling our 3e DM swearing over all the math he had to do to make our encounters challenging as we had a varied-level party of about 8 characters most of the time).
Here's the thing with party size- the more people there are in a combat round, the longer the combat round takes. This becomes problematic as characters gain more attacks and more abilities to sift through.
Even in AD&D, having 2 attacks per turn wasn't impossible with things like bows, spell casters increasingly got more spells to decide on whether or not to try casting, and if you're in a dungeon, chances a large party might not even fit in a room in order to actually take actions in a combat round!
As they game has progressed, the shift to smaller combats and party sizes is, IMO, a feature, not a bug, because it makes combats much easier to run on both sides of the table. When I was a DM back in the day, making my players fight two dozen goblins was just how things were done, but as I've gotten older, having to track that many NPC's and spending the time to chuck 24 attack rolls each turn gets tedious (and even in AD&D, weren't Fighters meant to blast through tons of low level foes anyways?).
So having a fight where it's my 5 PC's vs. say, three Trolls (where each troll has 3 attacks per turn) certainly saves on my cognitive load.
Of course, it's also true that PC's do have more things to track these days, with even Fighters now having "limited use" abilities on their character sheets. Whether or not that's a feature or a bug is entirely a matter of perspective. Some people are perfectly happy to do nothing but roll attacks each turn and not care about anything else.
However, even in the early years of D&D, players would often ask the DM if they could perform special maneuvers- they wanted to feint, parry, dodge, disarm, trip, cut off belts, and blind foes by putting their backs to bright light sources, slash foreheads, or toss sand in an enemy's eyes.
And it was up to the hapless DM to either make complex house rules, conjure rulings on the spot, or simply say "no" and carry on. Even by 2e, there was a host of optional combat sub-systems to handle most of these things, as the powers that be realized, this is what players want, and having some rules for them is better for many DM's out there than none at all.
At some point, abilities like this shifted from sidebars and sections of optional rules to living on one's character sheet as ever-present options. Again, whether that's a bug or a feature is dependent on what one wants from the game, but it's an obvious reaction to players wanting more "buttons" to push in combat beyond "well you see, you are doing all of that, but it's handled with an abstract roll of a d20".
And maybe it's just me, but I've found most DM's who prefer older D&D hate abstraction on general principles, lol.
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As far as "encounter budgeting" goes, the various "CR" systems are imperfect, because there's no way a game designer working against a deadline to fill a book with monsters knows what your personal group consists of- maybe you have three Paladins and a Wizard or a band of Thieves, or all spellcasters? Who knows!
Will they be built on point buy? Die rolling? Something else?
Will they have magic items or not? How good is their teamwork? Do they support each other, or is each PC an island in combat? Do they buff their stats or select various Feats? Do they optimize, or feel that "real Fighters only need Str 14, but ought have high Int and Cha!".
Etc., etc.. This is all well known, and is why published adventures become harder to write at higher levels- too many variables.
And yet, I try to adhere to encounter building guidelines as best I can, because as players become more complex, so do monsters. It becomes harder to eyeball what the party can handle. I've seen the same party blast through and struggle with variations on the same encounter, based on die luck, tactics, and terrain factors that "CR" can't even begin to account for.
However, by adhering to the rules, I at least know that I tried not to outright murder my players (no matter what they claim- according to them, I always hit with every attack and deal 25 damage per hit!). Because murdering players is easy. Getting them to actually face a handful of battles without running to flee and sleep after an hour of adventuring is not.
A lot of this has to do with the fact that I know I'm a hack DM. The social pillar is largely nonexistent. I rarely roll dice or consult NPC interaction tables. Most of the game takes place in the field, on adventures.
The exploration pillar generally comes down to rolling dice to deal with traps and hazards- puzzles and riddles are either easily solved by my players or they sit around for over an hour overthinking something I thought was obvious.
So ultimately, the exciting bits are the battles. It's what they seem happy with, since they keep asking me to DM. I wish I was a master DM who could navigate complex social encounters or have fiendish and diabolical puzzles to figure out, but I'm not. I've tried, and I just keep whiffing.
So better to stick to what I can do than not. Which is beat my players into paste, but try to be fair about it.
