I have two Kobai plants in my garden. When I first received them and during the first year, they had some dead branches. But they were small plants. At the moment, they have recovered fine. They are slow growing. They aren't as vigorous and don't seem that robust. But right now, they seem perfectly fine and healthy. They have attractive dark foliage, are very compact, and the flower shape is quite pleasant. To me, Kobai is a bit of an enigma as I don't fully understand how it sits on the R.indicum <-> R.tamurae scale. As with many of the more modern satsuki, it is quite artificial and a milestone in azalea breeding. Which is also why it was used so often as a parent in newer breeding projects. It's a bit like Asuka, Suisen or Juko, in that way. Namely, in having many generations of cultivar in their heritage, making them far removed from the species that occur in nature, and achieving very artificial horticulture goals in their looks, and passing it on to future generations.
Chinzan is basically the contrast to this as it is a more dwarf variation of Osakazuki which is basically a pink selection of willd-type R.indicum.