Let's start with the social pillar. That's just ... the most bizarre pushback I've ever seen. With great rolls and the right background a Monk can be good??? Well, sure. If hamburgers had the nutritional profile of Brussels sprouts, then maybe we would all be healthier. As I wrote in the OP: "This is a forum. We argue. There will be people that argue to the cows come home that True Strike and Witch Bolt are actually the greatest spells ever if you just have this one specific use-case that they came across in their campaigns."
Hamburgers don't have the nutritional profile of Brussel sprouts thpough and never will. Almost every table has a guy who put up great rolls. You are acting like that never happens. It happens all the time, and when it does you can play any class and be good at anything.
Keep in mind as you read this reply your statement is the Monk can "never" be good at the social pillar. That is just patently false .... even on point buy.
First, and most obviously, it would never happen in a point-buy campaign.
That is a minority of campaigns I think and again "never" is untrue.
Second, the right rolls and background they'll be pretty good? You know that Monks need a high dexterity, right? Not want, need. And a high wisdom. Not want, need. And a high constitution.
Agree on Dex and Wisdom but they do NOT "need" a high constitution and as a matter of fact I have never played one with higher than a 13 Constitution in a point-buy game. When I have played point buy, assuming standard +1/+2 it is typically 16 Dex, 16 or 17 Wisdom, 12 Con, and either a 12 or 14 in Strength or Charisma. But if you play a Half-Elf you can come in with two 16s and a 14 Charisma on 21 points and still have enough for a 10 con and a 12 Strength, and then you can get two different Charisma skils through your race in addition to one or two from class and background!
Usually on point buy I play with a 12 in CON, but I have played a Monk with a 10 Constitution and was fine. I have played every class except Barbarian and Druid with a 10 Con and they were fine.
Almost no one "needs" a high Constitution in 5E, because at the end of the day 5E is pretty darn EASY. Ironically, I have never had a character of any kind with a 9 or 10 Constitution die. I have lost PCs although that is rare, but I have never lost a character that would have survived with a higher constitution.
Not want, need. That's three scores. And finally, because of saves, builds, physical attacks, and (ahem) athletics you want strength. That's FOUR ability scores.
Not constitution. You are just wrong. If you are on point buy you are going to need to make a choice between Strength or Charisma. You are right about that much.
Which means that every single monk I've ever seen has relatively low charisma and and intelligence. Maybe they don't "dump" it. But they aren't high. Not to mention the monk has no class access to face skills. None. And no class, or even subclass, synergies with charisma.
First off if a player has great rolls he is not going to have a low anything and that happens .... often. Second a Monk can take one or more face skills with almost every background.
You have to actually try hard to build a Monk that can't take proficiency in a Charisma skill. Folk Hero is the only background in the PHB that does not offer at least one Charisma skill for a Monk RAW. Pick any other background from the PHB or the vast majority from any other source and you can get at least one of Persuasion, Intimidation or Deception on your Monk ... and often both. That is before you design your own custom background!
But sure, let's take your Witchbolt scenario. Let's say we are building the Face Monk because we can, and we like to argue on forums despite not really playing monks. Well, then we run into the next issue. See, D&D is a party-based game. And approximately ALL THE OTHER CLASSES are better at this than Monks.
Rogues, Rangers, Bards, Warlocks, Paladins and Sorcerers are inherently better because they have expertise or their other abilities mesh, but nothing makes the other classes besides these 6 inherently better than a Monk at Face skills.
That's right, the Warlock, the Paladin, the Bard, and the Sorcerer
That is 4 of 12 classes and pushing Charisma will not keep them ahead of proficiency .... and that is if there is one in the party.
The best faces do not actually include Paladins, Warlocks or Sorcerers though. They are second tier (although ahead of the Monk). The best are Bards and Fey Wanderer Rangers, the latter because they can add both Wisdom and Charisma along with their expertise. These two are really in a class of their own when it comes to face skills (excuse the pun).
So if you've ever played a Monk, in an actual game, with actual people, you know exactly what I'm talking about. The Monk will always be terrible at the social pillar. Is it possible to build a Monk that is merely "not-terrible" at the social pillar but sacrificing a lot of stuff? Sure. Just like it's possible for True Strike to be an awesome spell.
The last Monk I played was not terrible. The Wizard I am playing right now is far worse than my last Monk was. The last Rogue I played was worse than my last Monk too.
As for the second- again, as you correctly note, acrobatics "is not used that often" ... which is the problem. All of the things that Monks are supposed to be good at are lazily subsumed in Athletics- what, Monks aren't good at running and jumping??????
They are good at running, and with athletics proficiency they are pretty good at most athletic and acrobatic things.
You are acting like the proficiency bonus does not count, it does.
But because athletics are tied into strength, most monks are not particularly good at it; instead, they are good at an ability that is almost never called for (acrobatics)- and completely forgotten about in the written materials that WoTC makes.
I do use acrobatics for Tumble quite a bit on both Wizards and Monks at low levels with low strength. Usually without any proficiency in it.
Which means that in play, you will continually run into the situation of having an athletics check for your monk (whether it's holding onto a rope, or some other physical feat) that you won't be particularly good at.
You are usually pretty good at it, unless you for some reason did not take proficiency in Athletics. I would not say "particularly" good at every level, but OK at low levels even with an 8 strength, and really good at high levels. If you start with a 14 strength, which is easy to do on point buy, you should be really good at all levels.