That's not technically correct because you're not accounting for the fact that both, and everyone else, is on the motorway at the same time. That's where poor calibration becomes a problem, you're not just accounting for Bob racing his rice-rocket down main street. You're accounting for the fact that while Bob is doing that, traffic lights are going off randomly, other drivers are on the road, pedestrians are trying to cross and there's the occasional emergency vehicle roaring through.
A single kobold or a single dragon might be well balanced and fitting for its CR against an "ideal" and prepared party. But once you start throwing in bugbears, efreets and lair effects, CR becomes unwieldy because a "challenge" is not a linear, mathematical concept. A single kobold may be a CR 1/4 but 6 kobolds could be a CR2 because the tactics they can employ and effects they can take advantage of increase non-linearly with their numbers.
That's why its important to have a good transportation system, because you'll never know if the guy driving the big-rig is a kobold or a salamander.
The CR 1/4 number for kobolds includes the benefit from pack tactics. Without it (when they are on their own), their CR goes down to CR 1/8.
I would argue that CR is, for the most part, a single, linear, concept. Any anticipated benefits from team tactics that should be easily accessible (such as Pack Tactics) should be included in the CR number. Lair actions should be included in the CR calculation for the boss of the lair. Any unanticipated combinations and benefits from other monsters such as bugbears and efreets should be placed along with terrain advantages as a bump to the overall encounter difficulty.
CR is just a building block. The creative stuff goes in encounter building/balance.