In terms of the UI however, it's definitely very out of date.
When I upgraded my camera, one of the advertised features of the new one was that they added an extra digit to the internal intervalometer. Instead of being able to go between 0-999, the new one could go from 0-9999.
The fact that this couldn't be a simple software update still astounds me.
Basically slap a fucking android phone on the back when browsing photos. Make it a separate CPU if necessary.
Embrace the 'casual camera' body style more. The viewfinder should not be a big chunky thing in the center, but on the side and a pop up if necessary. Get rid of grips and make them a uniform rectangle, and add a battery grip in the box to make it slr grippy. People are scared of slr style bodies, while they are not scared of casual camera bodies.
They will continue serving the standard pro market who want the big chunky slr style bodies, this is how they can capture the 'high quality life memory / instagram influencer' market better.
Canon, Nikon, and others have long decided they can’t and won’t compete with smartphone makers and are increasingly moving up-market to the prosumer and professional markets who want “big chunky SLR body styles”, and they use specialized software like Capture One and Photo Mechanic to view/edit/organize photos anyway.
These days when the shot is easy the phone is at least in the ballpark with the big guys. When the shot is hard the phone isn't even in the running.
It ran full Android, you had all your file management, Bluetooth and wifi, could play games if you felt like. Could encrypt the filesystem, too, which I think is super important for journalists.
Basically nobody noticed or cared.
And yes, the high-end full-frame DSLR costs are on par with high-end laptops, but IMO you get 90% of the benefit for a fraction of the cost with an entry- or mid-level crop sensor.
As for the UIs, I'll definitely acknowledge they could stand some updates, but the way you describe it sounds like an overstatement. What would you improve, exactly?