Single saving throws

It's been a while now that my D&D-style games have used a single saving throw.

Original D&D's saving throws, with their more concrete categories like spells, death ray, and petrification, always seemed a bit limited to me, and since the 2000s (with 3rd and later 4th edition) the idea of having a save for reflex, another for willpower, and another for physical resistance made more sense. 5th edition, with its ability-based saves, seems even more direct, removing the need for the reflex/will/fortitude "middlemen."

But even that distinction eventually became somewhat pointless to me.

First, let's discuss the method behind saving throws against dangers such as like petrification, spells, etc. Contrary to what many claim, they don't actually distinguish well between classes. Thieves, for example, are NOT particularly good against breath weapons, but they are against spells, and dwarves, with their short legs, once they reach high level, end up dodging dragon fire better than they resist spells.

Also, paladins have better saves dues to divine favor, and dwarves/halflings because they are small/hardy. So you can barely tell what the saving throws really are within the game-world.

Without actually looking at the tables, you cannot explain the rhyme or reason for saving throws. Even if you can, it is a rationalization rather than a reason.

Even in Basic and AD&D, saving throws were eventually affected by ability scores, adding yet another layer of complexity (first by Wisdom, than by Dex etc.). The idea of using a dexterity check as a saving throw also shows up very early in the game's history.

Optional rule in the Rules Cyclopedia

But let's say the original saving throws actually did something closer to what the classes suggest: maybe fighters more resistant to petrification, thieves dodging breath weapons, and wizards avoiding enemy spells.

The first problem would be edge cases like fireballs, which are spells AND supposedly can be dodged (and probably avoided by armor too).

The second is that this simply doesn't match the fiction found in Appendix N. Conan resists spells not by "blocking magic," but by being tough. Likewise, a dragon's breath can be dodged by a thief, but it can also be blocked, at least partially, by armor or a shield, or avoided with a spell. Remember: in Chainmail / OD&D, it's powerful fighters, not intelligent characters, who are able to detect invisible people (which could ALSO be a saving throw IMO).

In short, dangers don't correspond, in any precise way, to how characters actually avoid them, neither in fiction nor in reality.

On top of that, the differences between saving throws within the same class are minor, and can be summarized, as pointed out long ago on Delta's blog, as a bonus ranging from +0 to +4 applicable across all classes (which is roughly equivalent to a DC in contemporary D&D). So the tables are an unnecessary complication.

Of course, saving throws organized by danger category also fail to explain edge cases like avoiding falling into a pit, crossing a river with a strong current, or dodge a falling rock (which maybe should be handled as a trap instead, an altogether different mechanic). I'd also have to consider how PCs would deal with the lasers, radiations and psychic powers of my current setting.

A single saving throw also helps resolve several difficulties in one roll. For example: can you spot the trap before reaching it? And if you do reach it, can you avoid falling in? Or if you're bitten by a snake — can you see it coming, dodge during the attack, resist the venom in your own bloodstream through natural antibodies, or even mystically alter your breathing, power through it, and so on.

While I don't remember the exact 3e or 4e rules on the matter, I like that in 5e they at least tried to give the Fighters better saves altogether with the Indomitable feature.

My last attempt at having more than one save was diving then into Mental and Physical, but even that was not necessary. Does armor help or hinder your physical defense against dangers that can be dodged? Most D&D editions do not seem to take this into account. Do we even need a physical defense other than AC?

Well, maybe for poison. But even then, unless you use "save or die" poisons you don't need Constitution to affect it. Just save "save or lose 3d6 HP" and your Constitution and level are already taken into account to see if you'll survive or not. What about a form of radiation there bypasses HP? Well, is there any reason to think bulky fighters would resist radiation any better than mages?

Maybe we need a mental save for Charm etc.? Not a great idea either. In which setting or game would it make sense to a mage or other creature to easily mind-control a T-Rex of limited intelligence?

So, basically now I got every PC to have a single saving throw number. They are not always the same: fighters get a +3 bonus, thieves +2, wizard +1 (and yeas that means they are frailer against fireballs). Monsters work similarly to fighters, most of the time (so we barely need the 5e thing where monsters can resist 3 times, or the AD&D thing where monsters have a chance of ignoring spells - which might be an issue for another post).

It is been working very well so far, and that's probably what I'm going with from now on.

My question: do you see any advantage in having several saves?