Skill checks simply don't need to be all that common (I first wrote "shouldn't be", but that's my preference not a fact) in social interaction and exploration. You can just play the game, describing what you do, and unless the DM thinks the outcome is in doubt, stuff just happens. Having a class ability that gives you a bonus on social skills, or to navigation in the wilderness, might come in handy now and then, but most of the time you can just cruise along based on players narrating what they do.
A good idea or plan should be 95% of the work. The last 5% can get resolved by dice rolling. So if one class is 20% better at rolling dice...in some situations...that makes then 1% better at the non-combat pillars, in those situations. Use whatever %'s you want, but you still end up with a relatively trivial difference.
Most of it can be about your own creativity. That leaves a tiny bit reliant on mechanics.
My sense is that those who think the Fighter class is deficient think you need to make skill checks to have fun, and are rolling way too many dice.
I'd like to reply to this. I fall into the "Fighter is deficient" perspective (though "deficient" is a word I'd avoid because it's vague), however I do not fit that typification – I don't think skill checks are necessary to have fun, I actively DM toward
quality of rolls rather than quantity, and I believe creativity trumps rolling dice.
My perspective is that in modern D&D there's a problem (specifically, something missing) at the concept level of the Fighter class. In older editions, Fighters were explicitly tied to an evolution into "lords" and "barons", with armies and tax revenues. IME this had the effect of driving Fighter PCs to (sooner or later) engage with affairs of state, interact with noble houses, and lead soldiers into battle. It wasn't just an oddity that kicked in at 9th level, but a lens through which the player was encouraged to interact with elements of the campaign world, just as "Rogue" offered its own lens into the campaign world with Thieves' Cant, associating with shady characters, and always looking for the treasure. Yes, the Rogue has Expertise for high skill rolls, but the strong identity imbued in the Rogue's concept doesn't depend on that – it comes from that lens the Rogue class offers players into the worlds of D&D.
As play moved away from the strongholds & followers side of things, that part of the Fighter was understandably dropped. However, that removal affected the Fighter more than other classes because Fighters were so iconically tied to the feudal government (that was an assumed part of D&D settings of the era). Nothing was created to fill that void. This left the Fighter's concept as "person who excels at fighting", which really isn't saying anything since Barbarians, Monks, Paladins, Rangers and Rogues also are very good fighting. Even the 5e PHB doesn't really give you a definition of "Fighter", instead resorting to language like:
[SECTION]All of these heroes are fighters, perhaps the most diverse class of characters in the worlds of Dungeons & Dragons. Questing knights, conquering overlords, royal champions, elite foot soldiers, hardened mercenaries, and bandit kings—as fighters, they all share an unparalleled mastery with weapons and armor, and a thorough knowledge of the skills of combat. And they are well acquainted with death, both meting it out and staring it defiantly in the face.[/SECTION]
In other words, reiterating "a Fighter fights."
The Fighter is displaced from any culture. A Druid knows Druidic, a secret language, and comes from a circle of like-minded nature-worshippers. A Sorcerer can trace their bloodline (or magical event) to some aspect of the world, as can a Warlock with their otherworldly patron. A Barbarian likely has a tribe, a Rogue also knows a secret language connecting him/her with shady characters in the setting's underbelly, and so on for every other class. But this is no longer true for the Fighter. Its concept lives within the confines of initiative.
This is why, back in my old thread, I encouraged a shift in thought – when hearing the name "Fighter", for players and DMs to think "Warrior." Why? Because a warrior implies someone who is familiar with conflict at a much longer scale than "roll initiative", someone who understands the movement and disposition of military forces, who understands how to negotiate for access to resources with varied factions, to bind wounds, to know whether so-and-so marches under the Duke's banner or a mercenary banner, someone who has something to fight
for and defend, perhaps even has a whole philosophy pertaining to how they engage in conflict, etc. Warriors imply a place within a culture, specifically that the PC hails from a culture with a warrior caste/class.
For me personally, that's where the real issue lies. At the concept level.
EDIT: I've noticed very few single-class fighters playing & DMing 5e, compared to other classes which I've seen many single-classed PCs. My
hunch is this phenomenon has to do with many players
wanting identity & a lens providing connection to the world to be part of their PC, and that they often look to the character classes to supply that. Not finding it in the Fighter, they then multi-class. Or, worse, they "dip" into Fighter for a mechanical benefit.