Basically, by choosing a the type of the lowest-connected highway type, we are sometimes simply defeating route pruning so Waze will consider the route instead of rejecting it without due consideration. Even if nobody In their right minds would consider the segments in question to be as high a type as what we need to select, or even a highway at all. Even if the segments can't even carry the traffic they are called upon to carry.
Sometimes, the "local road" connecting two highways serves a function similar to ramps. Lots of states represent ramps on their FC maps similarly to how local roads are represented.
Ramps are routing neutral, and can be used to defeat Waze route pruning. But we've decided not to draw the connector roads as ramps (despite the routing-neutral benefits that would bring), because they are not ramps and also because they would look confusing in the app or livemap. So we have to pick the least-detrimental road type for the situation at hand. Or most beneficial, depending on your point of view or current blood sugar / caffeination level

.
If there were a checkbox for "this is an essential non-ramp connector road and is routing-neutral" by necessity", we wouldn't have to "lie" to Waze about road types, and put such confusing statements into the wiki to explain why we do it.