In Rang Ngao, Ken's role as Veekit was small and not that important. Rang Ngao primarily focused on Mootha/Moonin & Nappa battling each other out. So that's probably why KA didn't get the chance to become a koo-kwan from that lakorn..... but I did notice their instant chemistry in that lakorn though.I like Ken and Anne. They are very good and accomplished actor and actress. However, we cannot compare them to Nadech and Yaya. Ken and Anne become a Koo Kwan very late in their career. When Ken and Anne first acted together in their first lakorn Rang Ngao, they were in their mid or late 20's and they didn't get recognized as a couple until their second or third lakorn five or six years later. Om Ruk was well received and Sawan Bieng cemented them as a koo kwan. Anne and Ken have been in the ET a lot longer than Nadech and Yaya so it is not a surprise that they were recognized for their talents. Nadech and Yaya, on the other hand, became popular with their first lakorn together and their second lakorn individually. They were only 17 and 18 years old and just came into ET so it is understandable that their actings will not be up to par with Ken and Anne.
It is unfortunately for Ken and Anne fans because they become a Koo Kwan late in their career so we might not get to see them much because Anne is turning into a producer.