Need help checking if I'm missing something critical with HP revamp

[Theodoxus]

So, after running 5 campaigns into the upper teens and 1 to 20, I've come to the very personal conclusion that hit point bloat is my biggest buggaboo. With 5E specifically, but in general as well (particularly video games, where having lots of hit points looks impressive, but doesn't mean much as most things at your level effectively deal a percentage anyway).

Anyway, my proposal for my table is a comprehensive cut across the board. My players have expressed a tempered willingness to go along with this experiment, I think reserving the rights to "I told you so!" if/when it fails - they are particularly skeptical that there won't be a weekly TPK due to my modifications.

Ok, on to what I did.

Hit points are based solely on Con Score. At 1st level, you get your Con Score in HP regardless of class. You do get hit dice, which are used for healing (and other things unrelated to this change). You do not get your Con Mod added at 1st level.

Every level thereafter, you gain only your Con mod (feats like Hardy still exist, so you get 2 extra HP per level if you take it).

I also have a feat called Brute, available only at 1st level (I give feats out every odd level, regardless of race, so this isn't just Human centric). Brute adds your maximum class HD at 1st level (only).

What this means, is a Barbarian with an 18 Con, taking Brute, would have 30 hit points, gaining +4 hit points per level. And that's really the far limit I'm happy with when it comes to soaking damage.

Now, to compensate, I stole (and then modified) the saving throws from Pathfinder 2 - Critical success, success, failure and critical failure. For damage, this generates 4 effects: None, 1/10th, 1/2 and full. For status effects, immunity to the effect for the round, no effect, full effect, and auto fail next round (or extended by 1 round if it normally lasts 1 round).

I also stole PF2s +10/-10 rule for criticals. I think the players really like criting on a +10 - their 1st fight was against demon goats with an AC of 11, they crit three times. They didn't get a chance to play with saving throws though...

I'm not modifying the characters damage or save effects for things they do against monsters - A save (even critical) is 1/2 damage, full on a fail and double on a critical fail. Monsters don't get the +10 rule either. So, the players can just play the game with no real changes to the core abilities - all the modification is on my side - though it does mean PvP can get quite deadly, if it breaks out.

So, basically, is there anything that I'm forgetting? Maybe a low CR creature that suddenly got particularly powerful; a glass cannon that deals a lot of damage on a hit that might rip through lowered HP characters?

[Grod_The_Giant]

Besides the fact that your Brute feat will be a straight tax... Damage is the way 5e scales. In many ways, it's effectively the ONLY way 5e scales. Like, 75+ percent of stuff you get from leveling up boils down to "hit harder, get hurt less." But unlike, say, to-hit bonuses, damage abilities come in a thousand forms, meaning there's no easy across-the-board conversion you can do.

I don't LIKE to say "this won't work, you're rewriting the entire system," but... this won't work, you're rewriting the entire system.

For a more graceful alternative, I'd suggest looking at status bars that run parallel to hp. Maybe if you take 10% of your health in a single shot, you take a penalty. If you drop to 75/50/25%, you're at some penalty.

[Theodoxus]

Only 1 player took Brute... he happened to be a half-orc barbarian and it fit his theme.

The problem I'm trying to circumvent is dealing with characters with hundreds of hit points; where I have to throw larger and larger creatures; spell casters with massive blasts or Save or Suck spells that are annoying...

By 13th level, the players end up dictating the speed of adventuring. If they want a 15 minute adventuring day, they'll Teleport, Plane Shift or otherwise sit under a Mordenkainen's anything and wait it out. It's less fun coming up with ways to shut that down (especially ways that aren't simply deus ex machina), than to just let it happen. Yeah, they're novaing everything then healing up whatever HP I managed to scrape off.

The only time that didn't happen was in Tomb of Annihilation and Tomb of Horrors, but really, making another dungeon that bans Teleportation strains credulity.

So, I figure if their HP are lower, things are grittier. They're playing scared; and it feels more tactical and less Diablo 3 "Let's hunt loot!"

[Tyndmyr]

The problem I'm trying to circumvent is dealing with characters with hundreds of hit points; where I have to throw larger and larger creatures; spell casters with massive blasts or Save or Suck spells that are annoying...

If you're leveling up, and nothing about the feel of play changes, what's the point of leveling up?

Now, there's nothing preventing you from modifying hp if you dislike that, or players having the initiative, but what do you intend to replace it with?

[JNAProductions]

I think part of the issue might be giving each player 10 feats.

A feat is a BIG FREAKING DEAL in 5E. They are vastly more effective than Pathfinder or 3.5 feats. So of course your players are going to be stronger and better than normal.

And as for how to avoid a 15-Minute Day... Add a time limit. You get one long rest every 24 hours (or they take a whole week, if you use gritty realism), so if you have only a week to achieve your goal before Mount Doom erupts, suddenly you have to take on multiple encounters per day or you're fethed.

[Grod_The_Giant]

The problem I'm trying to circumvent is dealing with characters with hundreds of hit points; where I have to throw larger and larger creatures; spell casters with massive blasts or Save or Suck spells that are annoying...

By 13th level, the players end up dictating the speed of adventuring. If they want a 15 minute adventuring day, they'll Teleport, Plane Shift or otherwise sit under a Mordenkainen's anything and wait it out. It's less fun coming up with ways to shut that down (especially ways that aren't simply deus ex machina), than to just let it happen. Yeah, they're novaing everything then healing up whatever HP I managed to scrape off.
That's just how high-level D&D works. You're playing a quantitatively different game.

[Knaight]

Massively increasing HP is an extremely rare trait in RPGs, to the point of being a distinguishing D&D feature because of it. HP on the other hand is still extremely common, if just one of several common types of wound systems.

In short you're trying to pull a central and distinguishing feature you dislike out of one of but a handful of games that even have it, instead of picking any one of the enormous number of other games. Why?

[Composer99]

If you don't want to run games at the power level of high-level D&D because you don't like what the PCs are capable of, well and good, as far as it goes.

That said, modifying such a core and essential part of the system, with all the knock-on effects it might entail, seems like a very complex way of dealing with this issue. And, because it makes everyone a glass cannon, I'm not sure it would succeed. If anything, it seems to me that such a change would incentivise 15-minute adventuring days even more than normal.

Would it not make more sense to simply run campaigns that are designed to end once the PCs hit low tier 3?