well i can't say its accurate. only the devs know how the engine works internaly. I've made a few 3d engines ( no better then doom equivalent realy which is just a few steps away from quake).

biggest problem is how is the engine calculating for POV. most 3d engines even today rely on a ray-casting system of some form( direct x and direct 3D just makes it fesable to run a good framerate in realtime) which is a reversed form of your raytracing programs. ray casting is basicly draw a line/vector out from your character pov like going left to right, collids with a an object in the map calculates distance and off known data form the level info knows that its X high z wide.. so can scale the size of it to set the object persective wise on distance away. BSP / portals can precalculate much of this but moving /shifting changing objects ( entities) have to be calculated in run time time .

so anything NOT in your POV is not renedered/calculated. but internaly the program itself updates postional data during runtime.

a model has to be rendered face by face in runtime. mroe faces longer it takes
Now between rendering, data update behind the POV now you should see why most 3d games are made for LOW poly models. all them polys just add way too much exrta calculations to do.

you can pick up a few good books on 3D engine design. its allot of trig
especialy blackbox trig to help speed up the calculations ( like bit shifts and lookup tables)