Earlier quoted context omitted.
So the alternate modes are required for proper operation? Or will it fall back to a standard mode and still work?
That's not how alternate modes work -- there isn't really a "standard" mode. When you plug in a Type C cable the two devices negotiate (via a combination of passives and some active negotiation) what protocols you want to use. Yes protocols with an "s." Power and, say USB 3.1 v2, or power and TB3 or HDMI or whatever. Among the problems is you can have a cable that can't support a particular alternate modes, or can't…
Perhaps in the scope of large scale manufacturing, having multiple (redundant) connector styles is a low hanging fruit for cost reduction.
But it seems that there would be increased user confusion and technical support required. Very strange.