It's a theme you can encounter in a lot of martial arts contexts. You could say it is the entire lesson of Dragon Ball Z -- Vegeta exemplifies the ambitious hard work guts and glory approach. And it takes him very far. But he's always playing second fiddle to Goku's approach, defined by love, enthusiasm, and play. Likewise, Shifu cannot surpass Oogway.
It's a theme you'll encounter outside of martial arts, too. For example, high level hackers are said to be characterized by playfulness -- you find puns and puzzles and riddles and laughter, devouring of technical manuals like candy. There are rigorous hours of morally disciplined study, but this could not really be said to be the source of their power or the character of their existence. Sure, there's plenty of hard work, and it's unavoidable, but the spirit of love and curiosity and play and enthusiasm will take you much farther than the spirit of discipline and ambition alone.
I have a book about learning electric guitar that repeats the lesson. The author writes (in paraphrase - I don't have it with me at the moment), "In my experience, there are two groups of students of the guitar: those who practice a lot because they want to be good, and those who practice every spare moment because they literally would rather not do anything else. One of these groups gets really, really good -- I'll let you guess which."
Po has that. His authentic enthusiasm leads to a spirit that finds the suffering of practice to be light because he is so overjoyed that he is doing kung fu. It leads to an encyclopedic knowledge of the art because he would literally not rather be reading about anything else. He surpasses Shifu and perhaps eventually Oogway in subsequent films, entirely because this spirit leads him places that mere discipline and ambition never would.
Are his kicks as clean as the five? Never. That's not his strength. And to the film's credit, he doesn't skip the discipline and training aspect. But he remains physically a bit sloppy to the end of the series, and I think this is making the point that this is not what strength is. Po's strength is in his spirit, and this is what in the end makes him the greatest master.
I have always found his fight with Tai Lung a little unsatisfying, too. It seems odd that he's immune to nerve attacks. What, because he's fat or furry or something? What does that have to do with excellence? It seems a one off oddity, not a deep lesson. But the film is so philosophically on point that I doubt it's something this dumb. The lesson about the superiority of a spirit of play is so true to life that I have to think there's something here.
The best interpretation I have is this -- what we see with Po and Tai Lung might be metaphorically talking about a real life phenomenon: facing an opponent as overpowering as Tai Lung will absolutely sap the strength from your limbs if your faith is in your body and in your training. You think you're strong? He's stronger. You think you're well trained? Please. There will always be someone better, and when you face them, you will be paralyzed and weak by the knowledge of that fact. But if you are a lover of the art and it's something you cannot turn off, that effect does not work on you. You cannot lose faith because your efforts were never about faith. As hopeless as you may feel about your odds of success (and Po feels hopeless right up until the moment when he wins!), you retain your strength and alertness because to you fighting is not about winning -- it is about being who you are. The situation cannot change who you are.
> Hard training is not the only ingredient to excellence
It's not the only ingredient, but it is the sine qua non of martial arts excellence. When have you ever seen a martial arts teacher (of whatever martial art) value the slob newcomer over his hard training students? Most martial arts teach strenuous training and repetition.
You first build a foundation of solid work and training, and only then you can become the "chosen one" or the playful one. Po's merits are that... he's an optimist and a daydreamer, I guess? Who said none of the Five were also optimists, loved their art or had good qualities as well as rigorous training and excellence?
I don't think Oogway saw that spark in Po at the festival - that was fate and prophecy. But I do think by the cherry blossom scene, he knew what was going on. You don't have to train a lot to reveal a purity and intensity of love that will yield brilliance in time.
That's the part I found objectionable. It's that bit of Hollywood magic woo where the newcomer always "has it" and the long struggling devoted practitioners never have. It makes a nice story, but the philosophy behind it is weak, doesn't reflect the actual world and I find it disrespectful of actual practitioners (of whatever (martial) art).
One last thing,
> Hard training may be an essential ingredient of physical excellence, but it is insufficient for true brilliance in any creative field.
Yes, but before he drew doodles, Picasso was a master of more classical forms. You really cannot skip steps. You know the saying about inspiration vs perspiration (often attributed to Einstein, I think?).