tighter math still lets you manipulate the situation, and you still can fudge die rolls too.
You might actually have to do that less because you could better predict the outcome. If you vibe your encounters instead of giving them some thought, you might have to do it as much as before however, at least if you do not just manipulate the tough ones but also the ones that turned out too easy
tight rules do not mean things have to be challenging, it just means they are pretty predictable
As I wrote it is not just about that anyway. While I would prefer somewhat tighter math, there definitely is a limit to that, esp. with an attrition model, and I prefer that over an encounter based one.
The real goal is to not make rests the obvious best choice every single time, and to achieve that through mechanics rather than because the DM finds a way to have negative story impacts to counter the players innate desire to constantly rest, i.e. the players want to push on rather than the DM having to twist their arms for them to do so
As DM, I prefer tight math, so that I can better plan combat outcomes. If something goes awry, I can narratively explain the unpredictability as "verisimilitude" and even narratively intervene if necessary.
But I still prefer solid math.
5e makes an effort to be very player friendly. But it also needs to be easier to DM. Probably 4e is the best edition for DMs to run.
My favourite version of D&D is 4e D&D. It's maths is tight, it's game play is pretty intense, and it does not require the GM to "balance" the "adventuring day", because all classes are (more or less, and setting aside some Essentials classes) on the same recovery schedule.
I also find it very responsive when GMing. For instance, suppose that I think an encounter is stalling a bit, or is a bit of a cakewalk - I can easily introduce a new element (eg a terrain hazard, or a new creature, or whatever). And the system picks that up in a pretty seamless network of feedback and interlocking systems: the additional challenge yields additional XP, which affects the progress towards the next level and thus the placing of treasure parcels. If it tips the encounter over the level +4 mark, it also means that the single encounter counts as a milestone.
The resilience of PCs, especially from the upper part of Heroic tier, means that the likelihood of an inadvertent TPK is low. And if there is an inadvertent TPK, that is easily changed to (say) all the PCs being captured, and then the skill and skill challenge rules make escape easy to adjudicate. If a PC dies, it's even easy to have a patron deity intervene and Raise them - just dock the appropriate amount of gold for that ritual from the next treasure parcel.
It's also eas, in 4e,y to do minor rests - like spend one healing surge, or regain one encounter power - and easy to do medium rests - like
recover one healing surge, or one daily power. The uniform resource suites and clear relationship between abilities and recovery times enables this.
But the overwhelming evidence is that most of the people who want to buy D&D products from WotC do not want to play a game with this sort of tightness. They want the "balancing" of classes, of encounters, of rewards, and of incentives - including incentives to rest or to push on - to be in the hands of the GM. They want classes to have differentiated recovery suites -
a fighter can swing their sword all day, and the idea of player-controlled abilities to deliver blows that
really count (ie 4e D&D martial dailies) are seen as too "metagamey" or "unrealistic".
Once all this stuff is punted to the GM, I think the idea that the system will nevertheless dictate an appropriate adventuring day by dint of sheer mechanical structure is gone. WotC, in the design of 5e classes, have built on the legacy of 4e Essentials to provide classes with differing suites that will nevertheless be roughly balanced, at least in combat, under a certain set of parameters (ie the right number and difficulty of encounters, punctuated by two short rests). This has not caused uproar, because it is just a natural extension of the increasingly intricate dimensions of PC build that have been a part of the D&D legacy for a long time. (Beginning with classes like MUs, clerics, paladins and rangers.)
But the stuff about pacing, rewards, etc has been left sitting outside of the mechanical framework. It's "GM empowerment".