Arabic, Persian and Turkish may use different words for the same referent. If every expression possessed one unalterable natural bond with its meaning, this extensive cross-linguistic variation would be difficult to explain.
The appeal to variation between languages supports the role of convention. A speaker might perceive a meaningful sound quality in a particular expression, but that impression does not determine the lexical inventory of every language.
Learning a word’s meaning thus normally requires knowing the established use of its speech community. Any additional claim of intrinsic sound symbolism calls for separate evidence.