I think it's funny when people use the dictionary like it's some perfectly unbiased and authoritative source, rather than a compilation of how people use words
Sometimes if you're going to have a conversation you need to agree on what a word means. If there's any ambiguity, I'm going to refer to the dictionary so we can continue our conversation, not whatever you or I decide a word means. The dictionary should be the common ground on which we speak when we disagree, because anything else is madness.
Depends on what the disagreement is. If the disagreement is purely due to two parties misunderstand each other as they're running on different definitions then it makes perfect sense. You can't have a discussion if you aren't discussing the same thing.
Someone compared dictionaries to maps. If the map shows a street that's unusable or doesn't show a street that's clearly there and leads to your goal, don't trust the map over reality. The map needs an update and so do dictionaries
But even the differences between British and American English are in part out of the national need to separate from each other. English was standardized around the time of the American independence and the first American dictionary was oriented at the British one, later the same guy made a different one to set American spelling apart. Words for Granted made a podcast episode about it.
Have you ever met someone who's actually paid for a dictionary in the last several decades? I don't think there's a global conspiracy trying to sell them to people lol, you can access most for free fairly easily.