I never had any trouble with the GR07 (ver. 1 and MKII). I love the highs on both the KC06 and the GR07.
The KC06 has a wider sound stage than the GR07 MKII. They are also way more comfortable. The GR07 are a PITA to get a good fit -- you always have to fidget with them to get a proper seal. The sub-bass is better on the GR07 MKII, but some people might prefer the mid bass of the KC06.
A good part of how we perceive and rate IEMs depends on personal things, the size/shape of our ears, the stuff we listen to, etc...
For example, I have no problem at all getting a good fit and seal with the GR07 MKII (neither with the KC06). But about half of my listening is to classical stuff and the GR07's highs have a slight sizzle with violins that I find annoying. The KC06's highs can be a tad edgy at times, but sound overall cleaner.
On the other hand, the GR07 have indeed slightly more deep bass, but only about 10% of the stuff I usually listen to benefits from extension below 30Hz. So it's pretty easy to see why I personally prefer the KC06 over the GR07, while others may arrive at a different conclusion.