(I get it that the graphics engine is probably the same for schematics and layout, which IMO is a mistake, but that's probably KiCad's long legacy.)
I did not realize schematics entry and PCB layout had a common legacy in KiCad. To me they alwas felt like they were originally developed by two entirely separate teams?
What teams? The original KiCad was essentially developed by one guy.
And, I didn't take a deep look at the source code - especially recently - but this would be my guess that the graphics engine for drawing schematics and PCBs is essentially the same, or at least with a large chunk of common stuff.
Actually -- originally schematic and PCB
were two entirely separate programs. None of the features we take for granted (like clicking a footprint and having the schematic zoom to the corresponding symbol) were possible.
Work on PCB moved forward to take advantage of things like OpenGL and better rendering and speed and such. Schematic was not modernized as such. The two remained separate, with different rendering and all. This was the case with Kicad 4 and earlier "releases."
Kicad 5 was the first release that moved Schematic forward to OpenGL and put it on par with PCB. This was a development goal: make schematic and PCB work the same and work well together, like the Kiway messaging between the two so that selection feature I mentioned would work. (I think that existed prior to 5, I don't remember.)
Kicad 6 is much more evolved -- part symbols are finally embedded in the schematic instead of being referenced to the originating libraries, for example. Using 6 now I see that from the user's perspective it really is one program, with two views of the design (schematic, layout).
Thing is: this is all what the users have wanted since forever (other than a different library system, on which there is never going to be an agreement about "what is best."). The biggest complaints were that schematic and PCB
were separate and obviously so!
Anyway.