And if that is how you see social interaction in D&D, that's fine as long as you and your players agree.
I, however, don't like seeing very high DC's in a game with bounded accuracy applying to skill checks, for one, and for two, I like games where social interaction is possible without having to convince the DM that your arguments are exceptionally valid.
Because if players routinely encounter large chances of failure at attempting a thing, that teaches them not to do that thing.
I made the comment about Intimidation. People don't like to be intimidated. And will generally resent you for doing so. So not only are most NPC's going to be resistant to that line of social interaction, other versions of the game have gone so far as to say that after the encounter, they will be hostile towards you afterwards (which is simply counterproductive).
In fact, during a 4e adventure, I was once in a skill challenge to convince a powerful NPC not to screw over the party due to an incident we were enmired, through no fault of our own.
One of the options presented was Intimidation. A player roll a natural 20, but we didn't get a success or a bonus on other checks. When I asked about this, the adventure itself states the the NPC is immune to Intimidation.
As a result, I have learned to always use diplomacy and Persuasion. Every. Single. Time.
This is how players learn to play the game. If it can't be done, it won't be done. I've often listened to DM's wax lyrical about "why don't players try interesting things in combat? why is there no swinging on chandeliers or using the environment creatively?".
Because typically, you don't know what the impact of those kinds of tactics will be. You don't know what DC the DM will assign, or if the result is worth it.
You know what players do know? What their attack bonus is and what happens when they hit. And it doesn't take a genius to figure out what the AC of the target is.
And DM's don't get crazy ideas if the Cleric casts Bless to make it easier to hit high AC opponents- but using Guidance to affect checks all the time outside of combat, let alone during negotiations? They totally do, and there are threads on this forum that prove it.
You don't agree with my assessment of the game's difficulty, that's fine. But I want to point out how this worked in 2e, to give you an example.
If you have a Non-Weapon Proficiency in 2e, it has a check. It might be Intelligence -1. If your Int is 14, you succeed on any roll of 13 or less (ie, a 65% chance of success).
In 5e, a 1st level character would have a +5 bonus to an equivalent skill. To have a 65% chance of success, the DC would need to be 12.
Can you get a DC down to 12 using the social interaction rules? Well if the NPC is friendly, or if they are indifferent and you can present the DM a good argument. Even better if the DM rules someone else's argument/actions are worth a Help action.
Or maybe you have a Bardic Inspiration die, or the DM actually allows Guidance.
But that's a lot of if's and maybes to get a reasonable DC for a check.
Now, it's been said that there are times a check isn't required- that's great. But a scenario was presented:
You can do this if you roll a DC 20.
I objected that said DC 20 was a reasonable DC for player characters.
All this other "well maybe this or possibly that or no roll should be required" is irrelevant to my objection. The DC was set, I said what I thought about being asked to roll at that DC.
I'll reiterate, just so we're clear- if you're fine with the skill system the way it is, great.
I'm not, I gave reasons why. You can agree or disagree with my notions. I'm not really a maths guy, but I know there's a difference between having to roll a 15 at 1st level and a 9 at 20th.
And you shouldn't require outside factors or a rules kludge like Expertise to make those odds better. Either unbind skills or lower DC's. Or don't, but don't be surprised if the reaction is that some players stick to what they know will work.
