Which brings us to the second style of play of pre-WotC D&D: it's a style which uses the mechanical trappings of the first style, but not the other play procedures. In particular, it assumes that the GM is overwhelmingly in charge of deciding what the content is that the players (via their PCs) encounter and hence engage with. The Dragonlance modules are a famous and fairly early published example of this style; the whole Planescape and 2nd ed Ravenloft ouevre is a highwatermark of it in pre-WotC D&D publishing.
In this style, mechanics often become secondary: the players don't use mechanics to gather and act meaningfully upon information (because the sequence of content is in any event under GM control - a hallmark of this style is that there is a clue, but then if the players don't find the clue a NPC tells them anyway); the players don't use mechanics to gain access to the content, but rather it comes to them as the GM dictates; and the one place where it is often assumed that mechanics will be deployed - ie combat - the assumption is that the PCs will win, such that if in fact they lose the whole adventure goes off the rails or grinds to a TPK-induced halt (and there is often an overt or covert signal to the GM that s/he should fudge combat outcomes to make sure this doesn't happen).
[MENTION=16586]Campbell[/MENTION] made a good post about this playstyle in a recent thread - summing up, in this second playstyle which downplays mechanics and relies heavily on GM control over the sequence of events in play (what content is introduced, and how the players' interactions with it via their PCs ends up), the players' main job is to provide colour and enthusiastic engagement with the GM's story.
My suspicion is that quite a bit of 5e is played in more-or-less this style.
<snip>
I think this is the true meaning of the slogan that 5e "puts poweer back in the hands of the GM". Or of [MENTION=996]Tony Vargas[/MENTION]'s remarks that balance in 5e is on the GM, not the mechanical design.
But failing to do this is not problematic if it is assumed that the GM, in any event, is in charge of managing the outcomes of encounters and feeding from one to the next. <snip>
If we assume that the GM is in charge of managing those outcomes and shepherding the players (via the PCs) through his/her scenario, then the fact that an encounter takes one or three rounds is just another one among myriad factors that the GM is managing, fudging around, etc. For many D&Ders being able to do that sort of thing is what they mean by "being a good GM".