It's probably not a bad analogy in terms of the "colour" and the sort of "construction" of the overall sound.
However, the intake contributes to the "rhythm", too, so it's like two orchestras (or groups of instruments) playing perfectly out-of-time with each other, in a pleasing / unnoticeable manner.
Consider the inline six, some are smooth in texture on the intake side, others are somewhat more rough / rhythmic. And it's entirely down to the intake configuration "translating" the engine's configuration / firing order.
But even with the smooth sounding ones, with the right exhaust note, it can all come together nicely. It's worked for Porsche in recent years, certainly, whose boxer-6 intakes sound very smooth, for the same reason the 330i above does (and the
Toyota 86, too, as compared to the typical
inline 4; they can be made to sound alike). You can do the exact same thing with exhausts on those cars; in fact the stock exhaust manifold on a
2JZGTE is the equivalent of the 330i's intake manifold, in terms of the "rhythm".
I don't know of a very efficient way to provide that level of customisation, though, even assuming the sound generation method can account for it automatically. I mean, how do you let people make what they want in a simple and intuitive way? When I do these things (like making a straight six sound like a 350Z, say), I have to draw it all out to work out the precise configuration, often getting it wrong several times in the process. It can also be very easy to come up with something that is either very difficult or near-impossible to actually fabricate in the real world, so that's its own issue for a supposedly "realistic" game.
Those modifications would be as distinct from any sound changes due to cams or compression or forced induction, etc. (although typical exhaust configurations for turbos are the way they are for packaging reasons, and that's why they sound the way they do, generally). I think that's better than lumping all of the changes into just "exhaust". Having the game react to every subtle little change like that would be something of a dream. But that's a bit harder to do than simply changing the exhaust configuration, which can even be done with traditional samples, with a bit of trickery.
