5E Math

A part of me feels ability score mods are too powerful in 5E, and they are thrown around for little reason other than to get characters to a certain baseline of damage. A good example is finesse weapons, which allow a wielder to replace their damage modifier with DEX instead of STR.

Proficiency? Add your mod to a skill roll.

Mods are passed out like candy.

I have never seen a game so focused on modifiers as 5E. As a result, the hit point and damage scale of this game are double B/X. Comparing monsters between editions hit dice/points are about doubled, but due to the game's bounded accuracy rules, ACs are way too low at higher levels compared to B/X. You need to figure the max proficiency bonus in 5E is +6, and in Swords & Wizardry, it is +13 for a fighter at the 20th level. So doing the math...

5E HD / 6 = AC adjustment for B/X (positive)

So if a monster has 20 HD in 5E and you want to use it in B/X, give it an AC bonus of (20/6) = +3, halve the hit dice for B/X and give it 10 hit dice. For attack bonus, recalculate that as a fighter of the same level in B/X, and either halve the attack damage or recalculate it by a melee weapon or similar attacks from monsters that level.

The math works in reverse too, so if you have a B/X monster you want to use in 5E...

B/X HD / 3 = AC adjustment for 5E (negative)

So your 12 HD monster in B/X should lower its AC by 4 points to be more in the bounded accuracy strike zone and double its HD to 24. Double all attack damage, or use similar attack damage from monsters closer to the original. Base to-hit bonus off a similarly leveled fighter, plus ability score mods.

DMs Can't Crit

You give the first-level character normal D&D starting hit points, and you double monster attack damage, and no wonder monster critical hits at low level are insta-killing PCs at too high a rate. You look at the 5E goblin attack damage, which is 1d6+2, for an average of 6 points damage (12 on a crit). If you got rid of the DEX finesse weapon mod and left it at 1d6-1, which is more in line with B/X, that is an average of 3 points of damage (6 on a crit). So Wizards says "DM's can't crit" as the solution in One D&D.

So they make another rule to patch the issue.

They completely broke the damage and hit-point scale of 4E by tripling the values, and they only half fixed the issue with 5E when they went down to a double scale. The original B/X math is fine, and it works, even without the "bounded accuracy" fix, which wasn't needed because the +30 and +40 to-hits were a broken part of 3 and 3.5E, which broke the game in many other ways they are still trying to fix. 

I love the game, but the math is atrocious compared to the original editions.

The B/X Math is Good

They mess with the damage and hit point scales - and the to-hit modifiers - to break compatibility with B/X, and frankly, B/X had the math right in the first place. Gygax and Arneson knew those dice, they knew to keep hit points low, and they knew that out-of-control damage and ability score modifiers would completely break the game. And the more you mess with it, the more rules you need to throw on there to fix the mess you made.

If you have a leaky pipe, do you hire the plumber who replaces the pipe with a new pipe the correct way; or the one who ends up using 20 pipes and six rolls of electrical tape?

3.0 and 3.5 introduced non-linear hit-point and damage scaling to higher levels, and that was a terrible thing. At the 5th level, you started opening up multi-attacks (and you still see this in 5E with action surges), and then you saw monsters at that level start to creep up in hit points. Back in B/X, this was a linear scale, 8 HD was about an 8th-level creature (depending on special attacks and defenses), and that worked fine. When introducing a non-linear scale to monster hit points, you need to invent new artificial rules like challenge rating - and patch and patch again to try to tell people how to balance encounters.

The original B/X math is the finest in all of fantasy gaming.

Monsters

An ancient red dragon in B/X can have 60-90 hit points and still be an end-game boss monster. A sword that does 1d8 is still a threat to that dragon. You give the dragon 300-600 hit points, and that sword is a joke. And then, you need to start throwing multiple attacks and damage modifiers on the weapon. Special conditions. Scaling damage with class abilities. And what was once a simple x + y = z formula turns into 3x + (10+y) + d(3b + 4c) - e = z formula.

In 4E, the ancient red dragon had 1,390 hit points, and the sword was a toothpick. Most powers in 4E were also toothpicks, including the dragon's own attacks. Combats took hours. And Wizards tested and approved these numbers. Yes, that team is not there, but it just goes to show you the groupthink the organization falls into, and they still make these mistakes (Tasha's unarmed fighters vs. monks, Spelljammer, etc.).

You go back far enough, and those issues do not exist in B/X.

They made some fundamental mistakes, and they have always kept up the non-linear scaling of monsters and damage as you go up levels. Even in B/X, your epic fighter gets one attack, like a +3 STR mod and a +2 sword, for a 1d8+5. No, that does not change as you go up levels, but your to-hit gets better, so you are landing more hits - one attack per turn. With editions past 3E, you see abilities increasing damage and also multi-attacks per round.

And those mods stack with every blow landed. Some estimates of 5E character DPS have 20th-level characters averaging 100 hit points damage per round (or more for some builds). Our epic B/X fighter is still averaging 10 points at level 20, but versus a 88 hit point ancient red dragon, that is pretty darn good.

I know, but that is boring to never increase in DPS! The damage scaling has been the secret sauce of D&D since 3.0 and is the main addition Wizards made to the rules. Before 3.0, we were focused on stories; after 3.0, we were focused on character power. And it comes at the cost of complexity - both in rules and balancing encounters.

B/X

This differs between the White Box style games (Swords & Wizardry) and modern B/X (Old School Essentials, Labyrinth Lord). I like the idea only fighters get damage bonuses from STR in the old editions, as it makes fighters unique. I have a feeling there are too many house rules in modern B/X that were introduced back in the D&D era (BECMI and others) that made the game easier, like giving every class the STR modifier to damage.

'But still, even allowing those house rules, the B/X math is far better than the scaling, non-linear, plus mod-heavy system we have in the modern game.

Less math, reduced modifiers, and lower numbers = a simpler game with fewer rules and, honestly, a better one.