That's a horrible undervaluation of what an adventure author does.
That's not the way it's always been. And it's not the way it is now. The adventure author is very influential on pacing.
Then I suspect we must have different ideas about what we mean by "pacing" in this case.
Does the author have influence on plot pacing? Absolutely. Does he decide that in this section of the dungeon there will be X number of monsters worth Y number of hit points? Sure thing.
But does he know how many rounds of combat it will take to get through that segment of the dungeon? Nope. Does he know how many healing spells can or will be used by the party during that stretch of the dungeon? Not in the slightest. That stuff is all guesswork, because its too fine in the details. Especially considering one party will go through with four players, two of which have healing spells... another with six players, one healer, and five different magical items... and another with eight players with not a single heal spell among them.
The best the author can do is use his brain and whatever CR or XP budget the game provides to give a rough estimate on the kind of fights he will write into the adventure for the "average" group. But we all know very few groups will ever be "average" and thus the pace at which they go through it will be all over the map.
So yes, to my mind adventure writers will not have to have such fine detail in the "pacing" of a 5E adventure where he needs to worry about whether the party will be using Basic game magical Cleric healing, or Standard game non-magical healing, or Standard game magical "long-term" healing or whatever other formats get presented. They won't need to present four or more different versions of every encounter to try and take into account every method of healing a party might have as they go through.
Instead, the encounter might be built on a budget of X number of XP... and the game may simply say that X equals an average encounter for a party of level Y. And if by some chance you're using such and such "gritty" healing method, treat the encounter as one level higher.
Those numbers denoting fight difficulty are always so fungible anyway based on party distribution that to try and build the game with any finer detail at massaging the number crunching is going further overboard than I really think it needs to.