This is unfortunate, IMHO. DSLR's are (far) superior in terms of battery life. This was inevitable, of course. It is similar to the transition from dumb phone to smart phones (which, interestingly, had a similar tradeoff!)
Mirrorless has several advantages: no more mismatch between the focus sensor and the CMOS sensor, no more mirror lag, viewable area matches CMOS sensor area perfectly, electronic viewfinder can show the image as it would be after exposure (making over/underexposed areas easy to spot while composing the shot), and most importantly it allows for much more compact lens designs because the last optical element can be much closer to the sensor since there is no mirror in the way.
Viewfinder lag has not been an issue anymore since 10 years ago. And with recent CMOS sensors having phase-diversity elements, autofocus can be as fast as with DLSRs.
I got the opposite kind of lens, one at the upper end of what you can wrangle in your hands. If your lens is big you have a heavy pack, look like a dork, can't hold it steady, all that. There is a lot to say for a camera that is easy to handle.
To take your SEL35F18F as an example, the lens weighs 280g. The Nikon DSLR equivalent, "AF-S NIKKOR 35mm f/1.8G ED", weighs 300g.
To go to extremes, Sony's SEL600F40GM weighs 3kg and so does Canon's "EF 600mm f/4L IS III USM" (admittedly, Nikon's equivalent weighs 4kg).
I'm not saying this to prove you "wrong" or anything, a Sony A7RIV weighs 665g to a Nikon D850's 1kg or a Canon 1DX Mk3's 1.4kg but switching to Sony might just be the difference between a 5kg kit and a 4.7kg kit: it's still pretty heavy.
I'm just pointing this out because when I was starting out I heard a lot of people talking about how small and light mirrorless cameras were. I think at the time this idea was focused more on cameras like the Olympus OM-D series. Amateurs/enthusiasts (including myself, who owned an OM-D) often didn't realise that one of the major reasons an OM-D kit was much lighter than a DSLR kit was that it was optically less capable due to the differences in sensor size. A big part of the reason an 17mm f1.8 MFT lens is so small is that it isn't equivalent to a full-frame 35mm f1.8 the way many people thought it was. It's more accurately equivalent to a 35mm f3.5 which could be made similarly light for the larger sensor, if anybody wanted that (but few people want that).
What they didn't point out is that those bigger heavier lenses are bigger and heavier because they are more recent, and the camera sensors are so detailed that the cameras need fantastically sharp lenses, which means that they are bigger. Also, people's expectations of the quality of lenses has increased. So, they could make some small light lenses, but then someone would pixel peep and complain about how blurry they are, when in actual fact they would be just as sharp as the old DSLR lenses, but the cameras are more able to reveal their shortcomings.
The accurate autofocus is nice but I would rather have an older flagship DSLR than any modern mirrorless camera. The only exception I might make is for a more recent Leica M camera, but that's only because I've sold one and would like to use those nice tiny little lenses again.
But are these lenses and bodies actually designed that way, or do they keep the old dimensions because of backward compatibility?
Battery life is much worse but when you go all in on next gen Mirrorless cameras there are gains that are just impossible otherwise in a DSLR. The thing that convinced me was using an A7RII 5 years ago in NYC at night. The simple fact of the matter was that the camera could focus and validate setup in the dark better than my own eye with my personal Canon DSLR, even with the wide open nifty 50. I think we are on the edge of major innovations in camera tech. The size advantage makes it easier to carry more batteries as well.
Really the biggest thing is that Nikon is just brutally behind in tech compared to Sony and even Canon. The market has moved past DSLRs. Sony showed up and showed how to do it and that was it.
I don't see how that is true in the slightest. The Z9 is a true flagship that stacks up well against the competition. Cameras lower down on the segment stack can also hold their own, albeit some would argue the autofocus is lacking. Autofocus is just one piece of the tech in a camera.
A lot? This must mean you get your info from Youtube grifters. Every serious reviewer has praised the Z9 for having world class auto focus capabilities that defy belief. People are panning tiny birds in flights and it just keeps hitting it.
The only criticism is that Sony has a tiny notch up in very specific situations, yet that gap is rapidly shrinking. We're talking really marginal differences here.
The annoying thing is that Sony simply cannot do software. I love my A7S2, the hardware is excellent even years past its release, but the menus are confusing as fuck, why does it even ship with WiFi with the option to connect it to an existing network when their own software can't detect it there, or why does it need yet another piece of proprietary software to be used as a webcam instead of just implementing USB UVC...
For a mirrorless camera the sensor and screen are on when you are setting up.
The flip side is that a mirrorless camera makes a great video camera with some caveats. For instance if you want to do a shot that smoothly zooms in or out you have a rocker control on a real video camera that you can hold steadily and it does just that. I can't do the same with a mirrorless lens because I can't turn the zoom ring on a lens very smoothly.
Furthermore, why are you unable to hold a mirrorless camera as steadily? Something like the Peak Design Clutch strap ought to remedy that I would think? Not to mention cameras like the X-T4 have quite good IBIS built-in to steady out the shot a bit.
Nobody is forced to make a sacrifice they don't want to. This is a complete win/win for the consumer.
This is assuming that you're taking pictures for a living.
(The smaller M43 lenses are a big part of why I use it, though, as I am a video-first shooter and Panasonic's video-friendly, silent-motor lenses are pretty ridiculous.)
And even when people are shooting with full-frame lenses (e.g. on Sony), they often use an APS-C camera body because it has more pixels in the very middle of the captured image, with the assumption being that you're going to be doing a lot of digital cropping anyway to get more effective zoom.
Plus I keep backups just in case my camera bag is stolen, and first party Nikon batteries are $70 per. I hadn't considered keeping a battery bank and a long USB-C cable as a backup though, so I'll need to look into that.