Actually no, I'm complaining about the exact opposite. I want to be working in spherical native coordinates, but QGIS seems to treat "degrees" as just another fixed unit of length measurement rather than an angular measurement!
For example I had the measurement projection set to "cartesian", which I would have expected to either give me the linear distance from (X,Y,Z) to (X,Y,Z), or the linear distance between the projection of those two points on an approximation of the earth's surface (either sphere or ellipsoid). Instead, it was treating (Lat, Lon) as if they were (X,Y) coordinates on a flat map and doing Pythagorean theorem on the angular measurements, resulting in the longitudinal distance being off by a factor of cos(latitude) !
I can see no paradigm in which such a result would ever be desired, apart from QGIS fundamentally working in terms of linearized projections, with WGS84 coordinates being added on as an afterthought.
Imagine you go on a road trip (along the surface of the earth). How far have you driven? In spherical coordinates, that's just changing two angles. In Cartesian coordinates, it's an ugly mess. Doesn't hurt that it's a lot easier to measure angles in surveying than distance.
However, certain GIS systems like QGIS and arcGIS are designed for making maps and have to display things in a 2D space. Thus, they have a projection mapping the spherical coordinates to Cartesian canvas coordinates and back again. This leads to unintuitive behavior, but it's mathematically hard to do better.
Now, the user interfaces and the terminology and the subtly disastrous inconsistencies between different data sources? Hot flaming garbage, all of it. These aren't problems with the underlying data models though.