And the much-vaunted optical viewfinders in SLRs and DSLRs give no indication of how bright or dark the picture you're taking will look other than from an exposure gauge. The effect of your shutter speed, f/stop and ISO are boiled down into an exposure readout as a number or the position of a needle, dependent on what parts of the viewfinder image are even taken into account.
In a electronic viewfinder (EVF) or with a LiveView screen you're simply shown how bright or dark the picture you're taking will look, making manual exposure intuitive.
Further, with DSLR's you can't even focus manually as a practical matter, as they don't have the split or microprism focusing aids SLRs had on their ground-glass, forcing you to rely on autofocus, even when it's misbehaving. With a mirrorless, if the AF system is not staying on your desired subject, just hit the magnify button and focus manually (keep your camera set for "back button focusing" so that the shutter doesn't trigger auto-focus, undoing your work).
The irony is that the Powershot "bridge cameras" with EVFs are actually much closer to the mirrorless experience in these respects than the DSLRs are!