I’m proposing a 5e Advanced or whatever that injects the balance and depth of 4e into the framework of 5e.
It’s an OGL project, not a GSL one.
Not a 4e a clone, but an OGL that's like 5e D&D but better?
But we already have 13th Age. ;P
I kid, but 13A did hit several of 5e's supposed goals more squarely than 5e did, supporting TotM, for instance, balancing classes with radically different resource mixes, for another, oh, and limiting the Xmass Tree effect, and mooks, and, well, more than a few, I guess.
The effect of the numbers in 4e, if you are working from the default Monster books and generally following the advice on encounter building, is that they progress the campaign through "the story of D&D".
Well sure, it was still D&D. Every edition did that, it just did it with varying degrees of effdup class balance, mechanical dysfunction, and smoke & mirrors. 4e just did it with less of the first and more of the last. I guess you could say there's a lot of valid distinctions among the various versions of the game (not just editions, but variants & such within each ed), but not so many meaningful differences.
In the classic game (the whole TSR era, so 0/1/2/B/X/Y/Z), class balance started broken, theoretically converged, briefly, in the mid single-digits, and broke again. PC/monster balance wasn't any more functional: you started with low-level frontline PCs very hard to hit for low-level monsters and low-level saving throws very hard to make, to high-level PCs easily hitting everything, high-level saves relatively easily being made by PCs & monsters, and caster power ballooning. The /numbers/ were complex: each class had it's own attack and save matrixes, with another for monsters by HD, all progressing at different rates by level, while class exp tables also varied the rate at which you gained levels by class /and level/. But, at it's core, as you went up levels, you hit a little more often per swing (and possibly swung more often), made saves more often, and you & your enemies had more hps and did more damage... but, damage from spells outpaced hp gains, while hp gains outpaced other most damage gains. It wasn't 'balanced' by any stretch, but it was messy & inconsistent enough that it was hard to concisely find "the problem" and /fix/ it.
WotC came in and 3.0 changed the dynamics. Now, everyone leveled at the same pace, PC or monster, prettymuch (a CR = Level monster by itself was meant to be a solid 'speed bump' encounter for a party of 5). But, bonuses were still different, BAB progressed at different paces, full, half- and 3/4, saves at two (slow and even slower) being completely outpaced by scaling save DCs (a profound change), PC hp gains peaked yet were outpaced by monster hp gains (monsters were calibrated as an individual threat to the party, they needed scads of hps), and skills... well, skills existed right in the core game and used a basically functional DC mechanic, which was a great leap forward for D&D, which had stubbornly resisted workable skill systems for 25 years, but they progressed at three wildly different rates - in-class, 1:1 & higher, out-of-class 1:2, and untrained: nada. The result, as with 'bad' saving throws, was stunning gulfs between 'best' and 'worst' in a party, making high-level challenges more problematic than ever (which is saying something).
At the start of the campaign, the PCs will be confronting kobolds, goblins and the like; at the end of the campaign they will be confronting ancient dragons, demon princes and the like.
Nod. And in the classic game, it'd be prettymuch up to how the DM ran things, but, in general, 1st level vs the kobolds and goblins it'd be a long slow grind of fighting, healing, fighting, resting, healing, resting, and fighting again, while at high levels it'd be a demented sort of rock/paper/scissors/wish. While in 3e it degenerated differently, with skills and conventional attacks rapidly going out of phase so that challenging one character left another non-contributing, layered self-buffing obviating that, and untouchable optimized save DCs obviating everything with a sort of rocket tag. But, in both case, in-between those level extremes there'd be a 'sweet spot,' where everyone was kinda on the same page as far as dealing with challenges (albeit in distinct ways, mainly by class) and the numbers more or less held together, with neither success nor failure seeming assured to the point of eliminating drama.
The point (and not the one I think I started out on) being, in both those broad cases and their many variations, the game played /differently/ at low level, in the sweet spot, and at high. Mind you, brutal at low level, workable through the sweet spot, and broken at high, but /different/.
In 4e, the most basic underlying mechanics - say, whether a given natural d20 result was a hit or miss, and how many hits it took to bring down the enemy - didn't vary wildly by class over levels vs same-level standard monsters. Some classes would hit a little better (like /1/ better, say, due to a martial class feature, or two or three better due to system mastery), some defenses would get neglected and you'd be hit a lot more by some attacks, but generally, pretty consistent way down at the engine of the resolution system. (Like how a engine going a certain RPM might be moving a car at 12 mph or 60, depending on which gear it's in - if all you have is a tachometer, it's the same.) So, yes, it stayed in that 'sweet spot' the whole time, but the differentiation of the phases of that "D&D story" is pushed out from those core mechanics.
Whether this is a good thing or a bad thing is (obviously) an open question - eg a lot of people praise bounded accuracy because it keeps kobolds and goblins "relevant" at mid and upper levels. But I think it's clearly a thing.
The desire to keep lower level monsters relevant lies, IMHO, in the genre convention of the mighty hero or wizard laying waste to many foes. In 1e, there was a special rule that let a fighter attack 1/level/round vs less-than-1-HD monsters (so not the Orcs Gimli & Legolas were mowing through, at 1HD even). Similarly, a Wizard could fireball By the time that really became mowing, the goblins & kobolds and whatnot had ceased to be much of a threat, and rolling all those attacks or saves just seemed tedious (once the fireball did double the monsters hps, though, you didn't need to roll the saves, it was auto-death, so /that/ at least was often still done, if very quickly), so what should have been moments of awesome would be pointless, hand-waved and unsatisfying.
If you could keep the lower-level hordes meaningful, so that it'd be worth it to play through the mowing - and more exciting than literally mowing your lawn - you'd capture a genre trope and a moment of awesome that would really add to the game.
So every edition tried to do it.
And every edition failed.
But, hey, at least they failed in a variety of interesting ways, that each had their own system-mastery rewards, amusing system artifacts, moments unintended humor, and opportunities for the DM to miraculously pull a fun session out of it in spite of everything.
5e BA fails (more of a partial success, really) by keeping the low-level monsters a little /too/ relevant, requiring rapid hp/dam scaling to model progression, and reverting to the save:1/2 mechanic for most AEs. So, when you have a high level party vs a horde of low-level monsters, the monsters are an overwhelming collective threat, because enough of them will be able to hit (or whatever) to pin-prick the party to death - if too many of them are left alive to act. While a top-level fighter can Action Surge and, probably hit & kill as many as 8 of the horde that first round, if that's, like, 10% of the horde, he's simply not doing the job fast enough. And, thanks to BA, he's not quite guaranteed hits. Conversely, if you can catch most/all that horde in a high-level (thus high damage) save:1/2 AE, it doesn't matter if BA lets some of them make that save, they're all dead. So the trope is finally enabled for the Gandalfs out there, but still not for the Gimlis and Legolases. (How's that different from the TRS & 3.x version, when the wizard could also just erase whole armies? Because the army is an actual threat to the wizard if he doesn't do so, post haste. That was the point.)
4e, of course, failed due to the illusion of the Treadmill, and TSR & 3.x due to lack of threat from the low-level hordes, as above.
(y'know, I think I may have slipped into a tangent or two there...)