Sorry, had to make this two posts because of a forum character limit
And unlike the Note, foldables have a number of downsides that are inherent to the form factor - more delicate screens, battery life limitations, cost.
This criticisms apply to phablets as well. The larger screens of phablets are more delicate, and present more surface area to be knocked by a hard object and crack. Phablets cost more.
Folding the screen protects it way more than any case or screen protector can. I mean, it's obvious, there's a reason the Nintendo DS was such a popular design for gamers under the age of 12 who are notoriously hard on devices. I don't even use a case for my phone, there is no point because the design itself is a lot less fragile than one that exposes the primary screen at all times. Yes, the internal screen of a foldable is more delicate than a slab. But here's the thing,
you don't expose the internal screen unless you are actually using it. A slab's screen is exposed at all times, and this is when it can get damaged. i.e. every single moment the phone exists. The risk to a foldable's more delicate of the two screens is only when that screen is unfolded. Which the vast majority of the time
not the case. For the majority of the hours in a day, that screen is closed and protected.
If you drop a slab phone, the screen will crack. This has happened to all of us. Think of how many times your phone has slid off a table or something. If you drop a folding phone, the screen is automatically protected if it's closed, and if it's open, the phone will likely even close itself to protect the screen (depending on how it's designed, and how it falls) because the hinge is smooth enough that it doesn't require that much force to close. You need to have the phone open and in your hand, and then more or less intentionally strike the screen with an object to put it at the same risk of damage as a slab phone. A very unlikely scenario.
Just look at your screen on time on your phone. It's only a handful of hours a day. And consider on top of that, with a foldable, the outer, more durable screen will account for a lot of those on time hours for a foldable phone. The actual risk profile for the more fragile of the two screens is way, way smaller than a slab phone's screen, so it doesn't
need to be as durable. The same way your lungs don't have to be as durable as your hands and feet, so doesn't need thick skin and an internal skeleton to protect it. It has your ribcage to protect it, so it's ok that it's fleshy and weak.
What is this battery life compromise you speak of? Have you actually used a foldable that you are able to comment on the battery life? My Flip Z4 has the best battery life of any Android I've ever used, and is comparable (or sometimes better) than the battery life of iPhones. A big reason the flip (as opposed to fold) style can have such great battery life is that you can use it in many scenarios without opening it fully, therefore, it only needs to power the smaller external display. It takes up a lot of the use cases of a smartwatch. You get the best of both battery worlds. A nice, big, power hungry display when you want to read something or watch something, and a small, power sipping display for everything else.
I watch YouTube hours a day, I treat it like a podcast. Yet I still get amazing battery life. I think I've charged my phone only a handful of times in the middle of the day, I usually don't need to charge it until after 9pm. The reason I get such crazy battery despite watching videos all day long while I work is that if I'm not paying direct attention, I can fold the screen halfway. The video plays on the top half in a much smaller window, and the bottom half of the screen becomes transport controls. With the black theme, the OLED display is only powered on for about 60% of its surface area. Hence, the incredible battery life even while watching video content. Do I love having a giant display to watch video? Of course. But do I need a giant display all the time? No. Then why should my battery
always suffer for the few times I actually want a huge display?
These are things people care about. The battery life is particularly germane to the Note compare because battery life was a huge selling point of the Note - the larger body allowed for a huge battery which people wanted.
Yes, they are things people care about, and these are areas where folding designs actually excel. Now that the engineering is mature, they are more durable than slabs. The fragility problem with initial designs wasn't the screen, it was the hinge. The issue with the screen wasn't fragility, it was legibility of the crease. But the weakness of the hinge was a mechanical engineering problem that has long since been solved, and it's a much easier problem to solve than increasing the durability of the screen. The screen doesn't
need to be as durable as a slab phone's screen, because it's closed for the vast majority of the time.
On these early models, if the screen broke, it was usually because the hinge failed in some way. It usually wasn't because the screen itself was exposed and cracked. The early hinges were not that great, and wouldn't even fully close so excessive strain was put on the screen. Not an issue any more, hasn't been for a few generations now.
The form factor itself lends itself to longer battery life. The cost has come down to the point where it is comparable to traditional slab designs, because again, the engineering has matured. You can buy a modern folding phone from a tier one OEM (Samsung) for as little as $600 MSRP. It's mature tech at this point. These things that folding phones are better at than slabs, all the benefits you pointed out about phablets, is why the folding phone segment is the only segment seeing explosive growth.
There are two ways to increase battery life. Either brute force it by shipping a massive, oversized battery (Note). Or discourage the user from using the device (iPhone). iPhones have traditionally had smaller batteries than their immediate competitors, but made up for it by software that shuts everything down as soon as possible. This is the design philosophy that folding phones engender. In the race to sleep, folding phones win hands down, and then do a victory lap. The smaller outer display with shortcuts to the most frequently accessed functions allows users to do their task quickly (check a notification, respond to a message, transport controls for media playback, initiate or pickup a call, etc) without powering up the hungriest component, then put the phone away quickly so even the CPU can shutdown.