Odd that you say “nearly all languages have”, which would include that other languages you yourself can think of, do not have “more sounds[…]symbols…”
The problem I have with “experts” when it comes to this kind of dogma challenging thing is that they are usually extremely biased and limited by that dogma.
Let me put it this way, if you saw those symbols on Mars, would you not consider them a form of communication or language. Ironically, to me at least, the limited ands relatively consistent nature of the symbols itself actually qualifies it as language, not disqualifies it.
Two languages I can think of that have approximately the number of phonemes that some of those sign lists have are Hawai'ian (at least 13 phonemes, depending on how you analyze vowel length and diphthongs) and Central Rotokas (11 phonemes). But that low a number is extremely rare among languages.
"...if you saw those symbols on Mars, would you not consider them a form of communication or language" Communication, yes. Language? Knowing nothing about Martians, I'd have to withhold judgement. On Earth, language is much more than just communication.