alt Hacker NewsOpenSCAD is all triangles and vertices. Fillets are difficult to do. Outputting circles/spheres generally requires you to for-loop over vertices a lot.
Libraries like build123d and cadquery use OpenCASCADE, a boundary representation kernel. You think in terms of the enclosed solid and perform operations - boolean add/subtract, fillet/chamfer, stamp text, etc - that return a new solid.
I'm not sure I understand your comment; OpenSCAD has functions like sphere(), cylinder(), etc. Most OpenSCAD models I have seen are built up primarily from solid primitives combined using boolean operations, just as you describe for the other tools.
https://en.wikibooks.org/w/index.php?title=OpenSCAD_User_Man...