And yet, doesn't this also fit the social aspect of the game? Instead of having some social-conflict-resolution mechanic or skills like bluff, diplomacy or intimidate, why not just have it part of player backstory (Ariadne grew up a noble's daughter, and has a good command of etiquette and intrigue), and just dispense with skills or mechanics?
1. Many people agree with you that the social skills shouldn't exist, since they overlap with the player's ability to roleplay their character as an effective liar, smooth talking diplomat, or intimidating thug.
2. Earlier in the thread, I wrote out a post where I discussed the reasons that I feel that a 3e style craft and profession skill doesn't make sense. Here's the list.
Me said:
To my mind, the failure of the 3e version of craft and profession rules was that:
1. Poor siloing. Having been raised as a blacksmith's apprentice shouldn't trade off as heavily as it did with things like learning to jump, swim, or climb trees.
2. Unclear outcomes. Not always true, but often true.
3a. Too precise. 5% increments aren't really necessary for most profession or craft skills. Is it really important that one character have a +12 at weaving, while another has +13 at fletchery? Probably not.
3b. Too precise. This is also related to number 2. Too much precision in statistics without much precision in outcome.
4. Take 10 and Take 20 made a lot of that precision pointless. This is related to 3a. Why differentiate between a +12 and a +13 if you're just going to Take 10 or 20 anyways and beat the DC by a mile?
5. Unclear overlap with a lot of other skills. The stereotypical example was Profession: Sailor, and how it affected all your other sailing related skills.
Combat, by contrast, doesn't have these problems. In order,
1. Its siloed pretty effectively away from other aspects of your character. The only major overlap are feats that could boost combat or could boost skills, depending on what you choose.
2. The outcome of an attack is usually the most well defined thing in the game, unlike a craft where its really not clear exactly what one can produce with a Craft: Weaving check outcome of 27 (a really nice rug? How nice? What does that even mean?)
3a and b. 5% increments in combat skill level are actually important, and increases in your skill combat skill level have discernible effects on your character's career.
4. There's no "override switch" like taking 10 or 20 that makes whole aspects of your character's combat skills stop counting.
5. Combat talent (almost) never overlaps with other aspects of your character's build in an unclear manner that makes it difficult to know which rules to use to handle a particular situation.
Social skills are a mixed bag.
1. They're not siloed away, but it seems more reasonable for your ability to be a smooth talker to trade away with your athletics skill since they're both adventuring type skills. Unlike profession skills which often punish characters for investing in their backstory, social skills get used more frequently.
2. Outcomes are usually clear. Less so than combat, but more so than Craft. This has a lot to do with the fact that the checks are opposed by someone's defense. A higher bluff skill allows you to fool more insightful persons much like a higher stealth skill allows you to conceal yourself from more perceptive persons. A higher craft skill, by contrast, allows you to make more difficult to build items... but what are those? Only DM judgment can really say.
3. 5% increments in skill level matter more because the check is opposed, and have noticeable effects on who you can lie to/ intimidate/ sweet talk.
4. You can't take 10. Take 10 is kind of the death of skills, because it bypasses them so completely. With a skill like Craft or Profession, where you can almost always take 10 (in the case or certain profession uses, you can't, but those uses also don't matter much because all they do is produce a little gold) what you've really done by taking 10 is turn the whole architecture of the skill into a basic "can I build this? yes/no?"
5. These also don't overlap with other areas of your character in confusing ways.
In partial summary, a skill check is useful if you need to know the answers to the following questions:
How often can I do this successfully? (ex: jump over a pit)
Can I do this better than someone else can perform a task? (ex: can I hide better than you can find me)
Its less useful for questions like
Can I do this at all? (ex: fix a broken wagon axle)
In that case, you can usually get by with a general understanding of what the character can and cannot do, which doesn't require 5% increments, etc, etc, etc. It just requires an understanding between the people in the game.
I think Craft and Profession skills mostly fall into the "Can I do this at all?" category. They're not things where you sometimes succeed and sometimes fail (because you take 10, which mimics the fact that in real life someone who knows how to make a cabinet doesn't accidentally fail every so often and have to start from scratch, he just makes the dang cabinet). They're not things where you are opposed by someone else (hypothetically you could have a cooking contest but generally you are unopposed when you build a bookcase or operate an apothecary stand). They are, in my opinion, better supported by simply roleplaying (winging it) than by utilizing the architecture of the skill system.