Regarding 6 seconds (in all the contexts) -- I don't know if it was the 120' move per 10 minute adventuring turn, or that speeds/ranges got cut in 3 when moving indoors, or maybe it was the AD&D 2e longwinded justification for why a combat round was a minute long. Either way, somewhere in the TSR era I figured out that time and distances (short of overland travel rates) were not taken all that seriously or at least favored game convenience over specific realism.
For that reason, I always considered a combat round to be 'the time it takes to a meaningful combat exchange or do something outcome-relevant' and treated that as a situational, unfixed, amount. Certainly knife-fights in tunnels under castles are going to be more fast and furious than mobile skirmishes and wildly faster than cautious formation fights or two entrenched groups behind cover trading potshots as the other sticks their nose out, etc. (yet they probably can all be represented by round-by-round combat).
So do I think some things noted as taking 6 seconds in WotC-era D&D are unrealistically fast? Yes, same as I thought some taking 60 or 600 seconds in TSR-era D&D was unrealistically slow. Usually it doesn't bother me. Honestly, I'm more focused on whether one should be able to do something in combat at all than a specific speed. Like, do we even need to be picking locks in combat? Was that something they thought they needed to give rogues (and did they think it was a major benefit to said rogues)?
as if these titles make any sense, add them to the annoying pile
Hero and Superhero made a lot of sense in
Chainmail when it took 4/8 normal soldiers successfully hitting one of them
on the same turn for them to drop.
Yeah, all of the golems are kind of weird. Clay golems not only have the power to reduce your max hp with a punch (Mike Mearls once told me it was because of "crippling force"), but they can also magically speed themselves up! Why? Who knows?!
Stone golems can slow people down. Why? This one at least gets an explanation: "Creatures that fight a stone golem can feel the ebb and flow of time slow down around them, almost as though they were made of stone themselves."
Iron golems can breathe poisonous fumes. Why? Who knows?!
I'm sure once upon a time, these abilities had in-game explanations, but you'd have to delve into past editions to find out what they were, since 5e's authors didn't seem to care to tell us.
Iron golems are probably an allusion to Talos, the giant metal* man who guarded the island of Crete in the Jason and the Argonauts myth (and more importantly for early D&D, the 1963 film with classic Ray Harryhausen stop-motion special affects). Talos in the movie didn't breath gas, it was filled with boiling ichor.
*in an iron-age Greece's telling of bronze-age Greece, making his actual composition realism/verisimilitude debate that predates D&D by over 2 millennia.
Them having a breath weapon fit well with flesh golems crashing through wooden structures and being healed by lightning -- undoubtedly Boris Karloff Frankenstein ('s monster) references. Stone golems getting slow effects... I suspect was just making sure each got their own special ability.
Here's another thing that has annoyed me for multiple editions now: the fact that D&D's combat rules always make dealing damage the most optimal choice. Combat will continue to be a boring, repetitive slog as long as players continue to view doing something other than an attack as a waste of their turn. Some editions have tried harder than others to give players interesting options along with dealing damage, but that hasn't always been received well.
I'd say 3e did a pretty good job of making just dealing damage to be the least optimal choice.* Yes, you usually have to eventually do damage and drop the other side to 0 hp to win the day, but it was the SoD/SoS/battlefield control that actually carried the day.*
*Certainly at certain levels and contexts.
Regardless, at a fundamental level, you are correct. Early D&D treated the decision to fight (/keep fighting) to be the fundamentally interesting decision-point of the combat game (with, for the tactically minded, a side-order of arranging to enter the fight with optimal advantage). Spells, magic items, and monster entry special abilities have always been confounding factors, but in general it held true.
Thing is, those spells are pretty big confounding factors. I've been playing bladelock/fighter-bladelocks for 10 years, and while attacking to do damage is still a major part of what they do, spending a round (or action surge) to cast
blindness/fear/hold person/hypnotic pattern is almost always part of the combat routine.
I think the place where your criticism holds true is for characters that want to do so with characters themed as wholly non-magical. And there, yeah, they tried a few times with 4e and late 3e (and even early 3e if you count adding in a bunch of feat-gated maneuvers and tanglefoot bags and other stuff), but it hasn't exactly hit universal acclaim. Mind you, interesting combat isn't a universal goal, and short combats seems to be another goal that lots of other people have (and the two, while not inherently opposed, have the capacity to negatively impact each other).