system
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human
CMV: The abundance of charisma-casters in 5th edition Dungeons & Dragons is a design mistake

D&D is represented by three major pillars which are used to approach the world and the characters in it - exploration, social interaction, and combat. Each class plays into one of these aspects more than the others, allowing players to choose what type of game they want to play. For example barbarians are great at combat at the expense of being much less powerful in exploration (no useful abilities other than braun) and socials (since strength and constitution trump all else). However apart from bards whose lore makes sense for them to be social butterflies (since they channeled their performing arts into magic), warlocks and sorcerers kinda stick out like a sore thumb. Indeed, their prevalence means that investing in social skills for any other class becomes a waste of time since the cha casters get both social skills AND combat power from investing in it. When was the last time the fighter was the party face out of a party of 4 or more people? Pretty much never.  

I think that this design decision interferes with RP, and for the rest of the party to ignore this design decision means significantly compromising their combat power for what is ultimately not an awful lot of gain. In my opinion, both sorcerers and warlocks should be int casters. This might run afoul of making them tread on the toes of the humble wizard, but if this is truly a problem then their designs should be diversified even further.
gpt
Maybe it helps to rethink the meaning of charisma in Dnd. 

It has less to do with social prowess and more to do with force of personality. It’s the reason why intimation is considered a charisma trait, and why charisma spell saving throws exist (you’re saving against losing your own state of self) 

Warlocks are defined by their relationship to their patron, no intelligence required to signed a contract with a devil but it may require a great amount of charisma to get what you want from such a deal 

Sorcs may have little to do with persuasion but they can shape magic by sheer willpower. Their magic is not a learned ability so it can’t be intelligence, but it makes much more sense if it was an aspect of their inner character, their personality. 

Dnd 5 has moved drastically away from the old era of dnd. Combat and Exploration are frankly not so important anymore, at most you may get one or two combats per session and most exploration is more abstract and loose than the multilevel mass dungeons of yore. 

Many players now-a-days are more interested by social encounters, and it’s unfair that for only one or two party members to have all the charisma power in their hands while others are forced to wait until they feel useful again. Therefore charisma is given a great boost and is more spread out amongst party members so everyone can feel included in the story. 

There’s also a reason why wizards are sole-intelligence classes, it’s because they’re frankly one of the most powerful and could be very prone to abuse with mulitclassing min-maxing. The game designers perhaps found it easier to simply keep wizards the only true intelligent full casters.