Text variables are much more powerful than you describe, although the simplest use case with project-global variables may be the most common.
Symbol fields can be used in the layout.
Hierarchical sheets can be customized:
The fields can be used as text replacement variables for example in symbol values (“parameterized sheets”). That makes real channels possible (otherwise identical hierarchical sheet instances but with different component values).
Enhanced bus handling isn’t mentioned.
You didn’t even mention (or did you?) the new editing paradigm in eeschema (being able to actually select items and act upon the selection) although it’s one of the biggest and most important changes. The old paradigm has been one thing which many new users have considered weird to say the least.
You mention Pcbnew -> Eeschema backannotation. It’s not completely clear but actually Tools -> Update Schematic from PCB is “backannotation” - the word means propagating annotations from layout to shcematic. With Geographical Reannotation the reference designators can be annotated in the order they appear in the layout; the result can then be backannotated.
It’s possible to create nets in Pcbnew (Inspect -> Net inspector). This makes schematicless designs possible without WireIt plugin (although attempts at schematiclessness by novices raise heated discussions in the forum because using schematic is usually better).
The graphic shape Rectangle is new in Pcbnew. Rectangle, circle and polygon can be filled or unfilled; in v5 they were always unfilled (although there was a hack to fill them).
The symbol editor has been changed as much as eeschema (especially the editing paradigm). Aliases have been replaced by “derivation”. Old v5 libraries can be only read and must be migrated to the new format to be used (just like the old schematics). Migration happens in Preferences -> Manage Symbol Libraries.
In the footprint editor the Pad Properties dialog has been redesigned, and there are new pad shapes. Custom shape pad editing has been changed. Rule areas (keepouts) can be added to footprints. Edge.Cuts layer can be used freely. Pads can be edited WYSIWYG as rectangles/circles.
3D models of footprints can be semi-transparent or hidden/shown. The 3D viewer has more options; raytracing has lighting options.
Just to mention a few…
We are still waiting for curves in polygons which is promised for v6. Also the content manager for plugin etc. installation which is in the list of v6 features not landed in yet is very important.
Copypaste works now even between program instances. Copying from one eeschema window to another wasn’t supported in v5. This is seemingly a small feature but may be important for some workflows.
On of the pet peeves amongst some new users (or those who have tried but not continued using KiCad because they don’t like it) is the coordinate system. It’s now possible to change it in Pcbnew to behave as most would expect.