Whether language's purpose was communication or thought is not easily answered.
For one, how would you know? It left no fossils, nor do we have any other kind of record from that time.
For another, the very question implies a teleological view of evolution, which is arguably wrong.
As for what 50% of people report (where did that number come from?), we have virtually zero intuitive insight into the inner workings of our minds in general, or of the way we process language. All the knowledge that has been obtained about how language works--linguistics--has been obtained by external observation of a black box. (FMRIs and the like provide a little insight inside that black box, but only at the most general level--and again, that's not intuition.)
Surely it's obvious that language production and perception evolved out of more primitive animal vocalizations, used for communicative purposes. How could it not have ?!
Note that human speech ability required more than brain support - it also required changes to the vocal apparatus for pronunciation (which other apes don't have), indicating that communication (vocalization) was either driving the development of language, or remained a very important part of it.
hot take: language's original purpose must have been to lie.
It doesn't take words to understand implication of a club in your hand and a body of dead ape. From there it takes either violence or words to defend yourself(rightfully or not). Here, using language to explain the situation is more efficient.
For one, how would you know? It left no fossils, nor do we have any other kind of record from that time.
For another, the very question implies a teleological view of evolution, which is arguably wrong.
As for what 50% of people report (where did that number come from?), we have virtually zero intuitive insight into the inner workings of our minds in general, or of the way we process language. All the knowledge that has been obtained about how language works--linguistics--has been obtained by external observation of a black box. (FMRIs and the like provide a little insight inside that black box, but only at the most general level--and again, that's not intuition.)