I mean, obviously, 5e doesn't support uberchargers or anything ridiculous, but high level spells that can trivialize or end encounters outright still exist. Concentration only goes so far, right?
It goes really really far, because it avoids the difference for a group between 10 rounds of buffing and surprise which could completely reverse the difficulty of an encounter in 3e. As for high level spells, sort of, because the opponents have them too, like in AD&D.
See I never had problems tracking all fiddly numbers on my sheet (though I understand why some people did! It's attack bonus vs. Thac0 all over again), since those numbers rarely changed, what buffs you received could easily be written on a notecard, and only an antimagic field was going to turn all the layers off at once.
The problem was that, with the incredible power of buffs, dispel magic and similar effects (there was a greater dispel for example), things kept changing, and that in addition to the duration of buffs, and the fact that sometimes they were applicable, sometimes not, etc.
I didn't mind removing some of those options, but it feels like, as a result, monsters are made with the idea players aren't receiving a given buff spell. In Pathfinder 1e, the developers made a big fuss about Haste- assuming that most parties would have it, and making sure weapon using classes benefited from it. This however created issues if you didn't have the spell!
Indeed, it was really something that I felt silly in 3e/PF/4e, this assumption that some buffs where there and that PCs had the right equipment. Really annoying and so glad that 5e got rid of all that.
I recently had it pointed out to me that a CR 17 doesn't mean what it used to be- at first glance, it sure looked scary, but then I worked out in my head how my level 11-ish Storm King's Thunder would fare against it...and the result was pretty well.
That's the problem of action economy combined with bounded accuracy. A single CR 17 is, on paper, a match for a level 12-13 party, but how many parties today really have standard array stats, no feats and multiclassing and no magic item of note ? Because that is the basis...
If magic items are optional, feats are optional, and the designers don't even assume a given party composition, it seems like just about anything could throw the math for high level encounters out of whack in 5e. Yet I keep being told that's not the case, while simultaneously having the old hands tell me that 5e is easy mode. So my ongoing quest to figure out "what's the deal with 5e" keeps running into snags.
The reason people are running into snags is because encounter calculation is incredibly hard to do in a non-calibrated game. 4e did it pretty well because it calibrated the PCs and calibrated the monsters and then it worked well when the monsters were about the same level as the adventurers. And that's it. After that, the encounter calculator works rather well if you don't forget to factor in things like feats/multiclass, magic items, high stats, synergies (and there are lots of them between parties, with foes, with environment,...), etc.
But it's also why the "adventuring day" is more about medium to hard encounters as a suggestion, because if one of these go badly, it won't go TOO badly. The idea is to have multiple encounters depriving the party of resources so that they can decide to stop when it gets too much. If you are pushing the envelope with only hard to deadly encounters, you are running the risk that an unseen synergy or stroke of bad luck pushes you into a TPK.
5e has many qualities for the type of games my friends and I are running, but people should realise that it is far less suited to Combat as Sport and tactical challenges, because it's more fuzzy and open-ended, and all computations of power are very imprecise on a system that is not calibrated.
