I don't think Seb's assessment is way off but he is failing to notice Jon's vocal improvement.
If 10 was Jon's worst hitting high notes, he moved up to an 8.
Now his middle range has really improved and what most of us are referring to. Listen to "Talk To Me" around 4:12 onward. Jon sounds amazing IMO.
You can't tell me that that wasn't smooth? And it really radiates being there live.
Now as far as one saying you can't judge by YouTube, they are more referring to the overall experience of the show. A lot gets drowned out between the crowd, the volume of musicians, etc. When you watch a video on YouTube, your focal point in 100% on Jon's vocal. Being there, is not the same. You people watch, sing along, look around. There was so much I didn't notice until I watch the videos on-line after the fact. And yes, it was clear that Jon can't hit high notes but I did notice improvement and really enjoyed his middle range. In addition, Jon was relaxed and sincere.
After watching past KOS shows on YouTube, my expectations were low but being there live was a totally different energy and experience. Great acoustics, crowd energy, alcohol, as well as everything else going on around you does not come across on the YouTube videos.