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The root problem, as I understand it, is autofocus. The phase detect sensors need light; a semi-translucent mirror directs light away from the viewfinder and onto the autofocus sensors. To keep the viewfinder bright, then, they compress the image (reducing magnification, as you say), and also changed the focusing screen to one that transmits more light but does so by increasing apparent depth of field.
When comparing magnification numbers, it is important to note what length of lens is used. Some manufacturers use a 50mm lens at infinity on cameras with an APS-C sensor, just like what was the de facto standard in the film era; this gives the same magnification specification as a 135-frame camera, because objects in the viewfinder are the same size, but the size of the viewfinder is much smaller. To get equivalent numbers, the lens needs to be 50mm-on-135-frame equivalent, or about 35mm for APS-C cameras.
Manual focus on a DSLR is tremendously helped by using a manual-focus screen, like the Canon S-type, which some companies (focusingscreen.com) cut down to fit other brands of DSLRs. But for enjoyment of the viewfinder, a pre-autofocus SLR is hard to beat. (I moved to film because I loved that large viewfinder so much. I've done my best to not look through a medium format viewfinder, because they will be larger and more immersive still.)