Sorry, but being a resident of Langkawi for so many number of years, the best tomyam is still prepared by Thais. If you are ever visiting Langkawi, try those in the northern parts namely Padang Lalang and Tg. Rhu. They are not so dense as the one I see here. Even tomyam prepared by a cook on a live aboard fishing trip in Thailand taste nicer than those dished out in KL/PJ. I don't know what the secret is, really.

The 'tai chow' in KL is even worse, they use readymade tomyam paste which is readily available from wholesalers.
One fact that I did noted was, raw ingredients from Thailand (which is available in Langkawi markets) like tumeric, galangal, lime, lime leaves - fragrant leaves, coriander leaves are actually more fragrant than ours that I see in our wet markets. even the santan are better there. Maybe that's the secret.
Sorry, I really cannot accept tomyam with santan.

In Hadyai you can even order tomyam without the chilly oil on the soup. The colour is like a normal soup but taste heavenly just like normal tomyam, sour, hot, a tinge of sweetness and saltiness and fresh prawns all in fish broth.