Beginner's question: opinion on cropping

... who is able to understand the full breadth of photography, both as a discipline and an art form.

One frames in-camera to maximize resolution with a single capture. That's it-- that's the only reason. Failing to maximize resolution with a single capture is not "admitting failure as a photographer".

Some reasons to crop after the fact:

1. One takes images of moving subjects, where one's ability to compose on-the-fly may be limited by neural processing speed, dexterity, and/or the need for accurate autofocus. Shooting moving subjects often involves a heavy amount of culling and adjustment, even if one has quite good timing. In this model, one exerts photographic vision in part by choosing certain shots after the fact, and reframing them.

2. One's camera records images in a different aspect ratio from that of the desired final output.

3. One simply realizes during processing that a better framing exists, and can't go retake a shot. Is having a superior artistic vision after the shot being an utter failure, or is it a growth of sorts?

Not everyone is a set-in-his-ways landscape photographer. These words are as kindly meant as possible. Shooting mostly static subjects such as in landscape and architecture photography lends itself to a more highly methodical process and a contemplative approach at the time of capture, but they're not the only types of photography that matter.  Nor even there does your advice make sense across the board-- small amounts of cropping that may occur during stitching, for instance, don't make one a "failure as a photographer".  The idea's silly.