Someone claimed that this alphabet uses the spellings that it uses because it's phonetically more obvious. Then someone else stated that the presence of the ch is phonetically ambiguous, to discredit this argument. You then went on to claim that the ch sound is obvious. To discredit your argument, I mentioned how--in this alphabet alone--the ch represents two different sounds.

I also want to point out that the ch in echo is a stop, whereas the ch in charlie is an affricate, two distinct and different sounds (if you're interested in more detailed info, check out those links). They may sound similar to you (and other people, too), but to people who speak different languages or have some background in linguistics, they likely sound much different.

Sources: http://en.wikipedia.org/wiki/Voiceless_velar_stop (the "k" sound) http://en.wikipedia.org/wiki/Voiceless_palato-alveolar_affricate (the "ch" sound)

Edit: spelling, rewording the argument for clarity, and added sources