See, you did know where to begin! Not so hard, was it?

The fact the stakes are high for the US does not translate into the region being dangerous, especially not imminently. Would not defending Taiwan destroy security guarantees in North Asia? It's possible, perhaps even likely, that the Senkakus would be indefensible if Taiwan is captured, which would weaken the US-Japan security relationship. But even this likely outcome still has uncertainty around it. The elites in Japan and Korea understand that their security relationship is far closer with the US than Taiwan is. Not to mention the fact that the US has made no security guarantee to Taiwan that promise to come to its defense, unlike with Japan and South Korea.

Outside of East Asia, I think this argument has no merit at all. I don't see why countries in parts of the world outside Asia would take the loss of Taiwan as a security threat. In fact, the US would be able to consolidate its overstretched military forces elsewhere in the world, possibly strengthening its strategic position.

As for why the South China Sea is more dangerous than Taiwan in the short- to medium-term, it all has to do with how much contact the US military has with the PLA in the region. Besides occasional transits of a few warships through the Taiwan straits by the US, there's essentially no contact between the US military and PLA around Taiwan. This makes accidents and escalatory dynamics much more unlikely. Compare with the South China Sea, where the USN and PLAN are regularly within eyeshot of each other, and where there's been many instances of near-collision and brinkmanship already. An accidental, unwanted INDOPAC war started by a collision between USN and PLAN warships in the South China Sea is much more likely than a Taiwan invasion scenario for at least the next half decade.