I remember overhearing a Best Buy employee describe the FireWire port on the back of an iMac as a Sony proprietary camera connector. Not sure why I didn't correct him.
Apple rarely goes proprietary with their ports. The original 30-pin iPod port. Lightning. ADB in the mists of time.
All of which were I believe better than what was available.
Lightning came out in September 2012 [1].
USB-C was ratified in August 2014 [2].
If we put the iPhone 6S model aside (because the -S models generally do not adopt a significant change in features), the only model released since USB-C is the iPhone 7.
Given the short lifecycle of phones, adopting lightning rather than postponing until USB-C has given several generations of phones with a superior connection.
Should the iPhone 7 have adopted USB-C instead of lightning?
Perhaps, but USB-C support isn't exactly widespread (and it might in fact be Apple which ends up pushing USB-C support to the point of widespread adoption).
Is the lightning connection superior to USB-C?
Well, it's size is smaller: 6.7mm x 1.5mm (vs 8.4mm x 2.6mm for USB-C); a 42% reduction in height, and a 20% reduction in width.
For devices like mobile phones, I can see how the size of connector can be more important than bandwidth or compatibility. I'd like lightning to be a standard, but it's definitely an improvement over micro-USB, and in terms of size, it's better than USB-C.
USB-C was on the horizon, but it was still years away when Lightning came out. I really think that Lightning forced the USB-IF's hand a bit and made sure that USB-C was a reality. Without a working example of how a reversible connection worked in the field, the USB-IF might still be waiting to push out USB-C.
Judging from the fact that people on this page are complaining about USB-C cables/adapters not working, and the non-compliant USB-C cable fiasco (e.g. OnePlus), I'd say it isn't that clear. For better or worse, you know exactly what you'll be getting with Lightning. The Lightning connectors are also mechanically very robust.
Of course, the one huge flaw is that now their phones and laptops use different connectors.
If my memory serves, lightning was introduced in late 2012 with the iPhone 5. I'm not sure we can really say that lightning was "on the horizon" that long ago. I would say lightning was "on the horizon" in late 2014, when in early 2015 we saw USB-C come to notable devices such as the Chromebook Pixel and 12" MacBook.
More likely than using any sort of standard port would be Apple inventing yet another new proprietary port.