The problem here is the knock-on effects from raising the overall difficulty of encounters this way. And with how variable damage is in D&D, that means you're very likely to have adventuring days where attrition is uneven from hard encounters. In effect, higher difficulty days mean you're going to do too much damage to some PCs and they will simply choose to long rest.
So, IMO, that was their logic during the 2014 playtest:
- The 5 minute adventuring day is a problem
- If PCs rested during the day, it wouldn't be a 5 minute problem
- We need the PCs to short rest to recover
- We can strongly encourage the PCs to short rest by giving classes abilities that recover on short rests
The first problem that they found:
- Long rests are really good because they fix everything.
- We keep having PCs take too much damage to justify only short resting
- If combats were easier, then the damage variance in the game would be reduced in severity
- Let's lowball encounter difficulty. Instead of 3-4, we'll double it to 6-8. Then we rename the encounter difficulty categories. Trivial is now called "easy." Easy is now called "medium." Medium is now called "hard." And hard is now called "Deadly." And the old deadly category is removed entirely.
Then, of course, they decided to
nerf short rests by limiting how many hit dice you get back. This has the disastrous side effect that the
one thing that long rests don't fix... is that you took a short rest. Thus, it's often still better to long rest because if you short rest then tomorrow you
won't be at 100%. The only attrition built in to 5e is tied to
short rests. Stupid.
The second problem was that they made 3 classes
extremely reliant on short resting (Fighter, Monk, Warlock) and then made 8 classes (Barbarian, Bard, Cleric, Druid, Paladin, Ranger, Sorcerer, WIzard)
extremely reliant on taking long rests. They needed 3-4 more classes to be more reliant on short rests and 3-4 fewer classes to be reliant on long rests. Oh, and Rogue, barring some subclasses, is an outlier. It's not reliant on rests at all.
The fix is that instead of incessantly punishing long resting -- time pressure, ambushes, gritty recovery -- that the game needs to
reward not long resting.