It's not about the graphics, graphics are often one of the most scalable aspects of games. It's mostly stuff like that GOW thing, needing those constant annoying hidden loading screens because the game needs to be designed for the slow HDD on the Ps4.
You still have to design new engines for an expanded sense of scale though. We're still working on first-gen PS5/XB Series engines. (Partly due to setbacks because of COVID, and GoW:R was supposedly targeting last year; also new engines are taking longer and longer to develop, you can see from how long it has taken for UE5 games to come out despite Epic hitting most of its milestones, in the gen before it mainstream UE4 games took over 2 years to come out; UE3 started after 1 year.)
...And then, you need to devise and experiment with new level design techniques which will work without the tried-and-true techniques.
Level gates like squeeze-through caverns or elevators aren't just there to hide the data loading. Yes, they can and usually are loading the next level in off the hard drive, and so that's one thing that forces this delay (especially on a HDD,) but lots of things happen to the game during these sequences that aren't data steaming. The lighting tends to get reset for the new scene, changing the color response and sometimes skymap for the look of the next scene. (People talk about "lighting" as just one thing, where you place your sun-source and turn on some lamps and everything is lit pretty if you do it well, but cinematic games have drastically different lighting set-ups for each scene, and even open-world games customize their lighting per zone. Fly across Horizon FW
and you'll see lighting and other effects like fog fade to change drastically as you cross biome lines even though the TOD remains the same.) Enemies or NPC get reset and locked out while parameters can be dropped and changed, making a clear and easy delineation in the game's level design for what happens on each side of the gate. (I would imagine it also helps save crashes if certain active elements can be cycled out when not needed, though I don't know if that juggling is really so challenging in a modern game structure?) Sound is reconfigured often in these gates, with tracks blending and new sound beds replacing the previous area's sonic signature. Sometimes the two pieces of level aren't even "lined up" as you would assume areas of a map would be connected, and instead your character is bamphed away during that load from one stage block to another. Lots of technical bits can be quickly cycled while your character is staring at a wall, even if it's just for a second.
You can see some of these aspects of what gets loaded and reset if you watch some of the Boundary Break videos out there.
And then, there's just visual impact. These cinematic linear action games want to wow you when you enter a new area, and so they use different sleight-of-hand tricks to distract you from what they're about to show you until it's ready to be revealed. Put a big mountain between a dark forest killing ground and a majestic bustling city filled with villagers and you have something exciting to see when you emerge from the cavern or cut through the ravine; if you can see the city off in the distance while you're fighting monsters, the effect is lessened (and it makes it weird that you're busting your ass smashing monsters while they're carrying water pots around town.) Put a dialog sequence where the camera is out of the player's hands with cropped closeups of faces, and the game can do some of this same loading/resetting while you're having that chat. Etc.
Even in a game where the loading is "instantaneous" like Ratchet & Clank Rift Apart, it still takes advantage of that transition zone when falling through rifts so that everything between the two levels works properly and looks visually appropriate. And in the Pocket Dimensions, it's possible to glitch the spaces so that your character travels from zone to zone and see the tricks they use to make these two realms seem seamlessly stitched together.
These stretches of playable game space that players think of as a "world" tend to actually be much more limited and unbuilt than you would think they'd be. Partly, that's a savings on resources, but mostly it's just how games are made and how it makes sense to build playable spaces to direct players for what they should be playing versus what they think is out there in this "world". It's Hollywood in digital form.
And to change that, it's not just a technical fix.
SSDs make the data quicker, but they don't make the design easier, or the new ideas on how to do brand-new sleight-of-hand tricks any simpler to come up with. If a game has a ladder which leads down into a dark dungeon, you the player know what will be down there and so does the level designer; make that dungeon entrance a big cave mouth and it's less clear what will follow you in or out and when you are in or not in the dungeon. There's the theatrical experience where the audience and designers are using the same understood concepts to understand the play space, and then there's the technical aspect where control needs to be applied to ensure a smooth experience. Of course, games have evolved past being that simple (caves for instance tend to just reset everything based on a threshold, and players understand that they've crossed a threshold based on the lighting,) but in some ways, they haven't, because what works works. New game design approaches and mechanics had to be devised as games went open-world, and similarly new designs will have to be explored as linear games pull out their stitches.