Of course, because they're full-frame cameras, the glass is still big, so you don't get the hyper-compact size of a micro-4/3 body+lens, but it's still waaay smaller than, say, a 5D + a lens.
I believe the equivalent APS-C Fuji 23mm f/2 is around 200g/0.45lbs.
Of course, with the Summicron you give up such new-fangled innovations as, say, autofocus.
The glass for my Sony A7ii is significantly larger than (most) lenses I had for my Olympus m4/3 body. The exception is the main prime on both systems -- I have the Sony 50mm/1.8, which is about the same size as the Panasonic/Leica 25mm/1.4 that filled the same role on my Olympus.
One is that many manufacturers haven't taken advantage of how mirrorless changes lens design yet (the shorter flange distance enables a lot of design space), so you're still carrying a lens designed for a DSLR, but with a lot of hollow space between the back element and the mount. This is especially obvious with third-party lenses; e.g. it's well understood that a lot of Sigma lenses for Sony FE are functionally just their DSLR lenses with a built-in adapter.
The other reason why you don't see a big weight advantage with mirrorless lenses is that, where they are designed for mirrorless specifically, they tend to aim for "better" rather than "lighter. Lenses like the Canon 85mm f/1.2, the 50mm f/1.2, and the 28-70 f/2.0 are perfect examples of this.
However, lenses designed to take advantage of mirrorless can be smaller and lighter, when they have the same design goals — e.g. the latest (DSRL) Canon EF 24-105L f/4 weighs 795g vs the (Mirrorless) RF 24-105L f/4's 694g.