Was I wrong though? (Genuine question)
You are right that people adapt their languages, but it’s always a complex thing. We constantly adjust how we speak according to context, especially the identities of our interlocutors. We may adjust our speech to be more similar, signaling group solidarity, or we may adjust to highlight differences, to exclude an outsider. One of the functions of language is to convey information, but that’s actually secondary to negotiation of identity. Before anyone is interested in the information we communicate, we have to assert ourselves as someone who is important enough to listen to. Bill Clinton was famous for being able to talk to anyone, he could adapt himself to any group and context. Donald Trump and Barak Obama were extremely skilled at talking to their supporters but the way they talked alienated a lot of other people. In Trump’s case, that was deliberate, he signaled solidarity with his supporters by highlighting how different he was from his opponents.