I have been digging though my books and I've come to a bit of a realization about this. It boils down to "add, don't subtract."
It's a losing proposition to mangle things in and cut things from the current edition to mimic the play of older editions. The players will rebel, the DM will be unhappy...and it will all collapse. It's a waste of time, really. But, instead, you embrace the thing for what it is. You as the DM can freely add material to the game and almost no one will complain, but if you try to remove things, that almost never goes over well. The book says the player gets that toy at that level for picking that thing. So let them have it. There's a few things that are just broken, that's not what I'm talking about. But the best solution seems to be: work around it. Add, don't subtract. Infinite dragons.
So instead of removing this or that, or mangling the adventuring day or destroying short/long rests to evoke a bygone age of D&D...you add to what's already there to get vaguely close to the same results. The numbers aren't absolutes. They don't mean anything in isolation. It's only by comparison to each other that they matter. That a 1st-level character has 1, 2, 5, 10, 20, or 75 hit points doesn't matter in isolation. It's only in relation to the monsters and their damage that PC hp matters. Through that context.
You want to make your 5E game more grimdark and scary...beef up the monsters to be nasty, dangerous, and challenging to baseline 5E PCs. Add, don't subtract. The players get to have the experience you're trying to give them while not having to deal with you taking their toys away. Just ignore that this is literally the escalation problem and likely exactly why we have the current issues with 5E. The designers just keep adding and adding and adding.
PCs blowing through your monsters? Add more. Beef their hit points. Drop some 4E monsters on their heads. PCs pulling a five-minute workday? Add more. The next encounter is beefed up because they waited an extra 8 hours before tackling the next thing.