I don't use any optional, variant or house rules. Reading what you're saying, I have to wonder what the last time you read the DMG on social interactions. Because it states that you may want to chat with the NPC in order to get insight checks to uncover their characteristics, that the DM sets the DC, that anyone who has participated in the conversation can make the check, that if another PC substantially contributes to the check the persuasion check can be made with advantage, there may even be multiple checks depending on the situation. There's also advice on targeting specific players so that they have a chance to participate "If a couple of players are dominating the conversation, take a moment now and then to involve the others." All from the rules.
Could it be better? Of course, and I hope the 2024 edition does a better job. Then again, I don't envy them because no matter how often they state "The rules are not in charge, you [the DM] are" some people will take any example they give as the one true way that the game must be played. There will never be enough advice to cover every situation. But discussing how the DMG should be rewritten is a whole other topic.