I have no idea how you create your encounters, or how you play, etc. I know that 90% of the time I build everything custom for my players. I have 3x5 cards for each encounter if there are 5 creatures it has 5 sets of ac/hp/weapons and saves. I do this for several encounters for each session (most do not get used) and if they did not level up I use the rest next time. I have boss monsters detailed out more, etc. Everything is tweaked live as things happen, so say they meet a group of 5 goblins with 2 archers, 2 fighter types and a caster (3x5 card has all that and a rough treasure list). The party kills half right away, IF I wanted a better encounter, I will pull another card and add a few from it saying they were holding back on orders.
If they are too much for some reason, I may have a couple run away to get help, allowing the group to kill the couple left and choose to follow or flee, Or I may drop the hp of a couple of them, etc. There are times when a player rolls well for damage or to hit (say the party is hurting badly and the fighter finally rolls a nat 20. The monster has 5-10 hp more hp than the final damage count ends up, i may still say it died, giving the fighter that awesome moment). But that is all live. It is not hard to have custom encounters, in a live game everything changes on the fly as players move through the world anyway. It just seems highly lazy to say "ALL goblins have 7 hp".
That said, I have zero problem with the HP I have seen so far in this game.
I think the difference is that it sounds like you alter encounters during the encounter to make adjust the difficulty- "The party kills half right away, IF I wanted a better encounter, I will pull another card and add a few from it saying they were holding back on orders."
Here is an encounter I have for avernus in one of my online games. This is a total bait because the little things explode and do acid damage when you hit them and they are rolling around in a mad max infernal war machine and would obviously lol and go for the run-over. Otherwise, this is realistically a fight against the Goristro and the
Chasme. Whatever this turns out to be, is what its going to be. They have the option to just bail if they want too. I set these up as "whatever happens, happens. Pretty sure they can do it". I have their character sheets and I can do all the DPR calculations in my head for what they'll do, take, and how many spells theyd need to heal worst and best case scenarios. I remove bodies when that extra 5 little shits might mean an extra 40 damage and drop 3 more spell slots because I have other things I want them to accomplish as well. Now, players exist, so they drive off (which they did) or they come up with something clever and steamroll or anything in between. For this meaningless fight, I have no interest in changing this stuff. The math is there, the fight will roughly accomplish what I need as far as an encounter and if they hadnt been pussies, theyd have gotten some rad shit.
Now, this is a boss fight. They walk in, there are 2 Erinyes that have been unchanged other than boths having whips that also act as ropes of entanglement. They get in a fight, one turns into a spider, webs someone up and is a pain in the ass while the other shoots poison arrows 40 feet in the air. Then they swap places when the other one gets hit back into form. If its going too easy, then 2 phase spiders burst out of the chest. Theyre not super strong but they will help diffuse the focus by the PCs. Depending on how it goes down, that lever near the coffin doesnt open the coffin. It open a rift into the underdark and a fomorian comes out. I have levers to pull now. But making the gals have 300hp so they get a chance to do more damage or making it up on the fly so an arachnomancer was hiding in the coffin and to just start introducing elements I havent done the math for...I like standing by my encounters and after a thousand + you can dial it in pretty well and not worry about it. I just have never been thinking "man, I wish I was managing individual health pools for all of these". Having a standard makes it so you can dial it in. Those weird swings in HP means a DM can't - as reliably - determine the math on the DPR.
In a game - you have to standy by whatever the hell you just put on the field. So the "computers can rando generate" thats saving about 5 minutes of rolling for a number of predetermined creatures that if you playtest youll just add more if it was too easy. And that is the point where, if you are doing that, why not just put standardized creatures in and swap a weakling for a tougher individual because now you are bloating initiative to make up for a line of glass cannons and you and looking for a certain difficulty. That is where I am, in the context of a game, not understanding that if they had a blank map why theyd make these particular decisions when they don't have the chance to course correct mid fight. Why not make it standard, repeatable, predictable - maybe not to the players, but to them at least. The original post was about how these changes may make the fight more dynamic or whatever they're trying to do, but what it does is, with the combination of the other elements of the combat system that have been introduced, to reduce efficacy of the PC abilities in sacrifice to this particular mindset they have displayed. As a DM, I would feel bad about it as it reduces the cool factor of their abilities and I want people to enjoy using those as opposed to dreading the fact it just isn't going to do quite enough (always a risk as a caster, but this is pushing it down more). That is why I don't see a justification for running it that way when they do not have a DM adjusting. It seems whimsical and I can't imagine what would be needed to be in my head for me to make that decision as opposed to just sticking with it. I just don't see the logic on starting from nothing and choosing that path. From what I can tell, the OP is correct in the ultimate impact of the decision and the questions have to be is that what you wanted to do, is worth it, and is that the best way to do so? Im having a hard time sitting back in my chair slow clapping and saying "You did it again you beautiful bastards, masters of your D&D craft".