Any discussion of charisma must take into account that it's one stat where there is very clearly a number of unmarked stat-checks. No doubt other attributes have them as well - they're tough to find, even with the code as (from what I understand) they're written into the specific encounters where they occur, and not the (more easily checkable) skill systems. That's why you can use a high-cha character to trigger the extra dialogue, and THEN switch to your dialogue skill character to use smartass/kissass (though there may be places where one character must pass both a cha and a smart/kiss check at the same time - there have been a number of semi-detailed reports of a particular hardass check only becoming available if you have a character with high str AND a decent amount of hardass).
If true, then it's gold to a guy like me who fucking loved the secrets of the old wizardry games, where it was considered a key part of the game to learn the specifics of what s stat/spell/weapon did (and many Wiz 1 players NEVER found out how to become a ninja, or even a lord). It's not like the games left you too blind to use tactics - you would start off knowing as much as a newbie could handle (str increases danage and to hit, con increases hp, etc), then you start working out subtler effects, and by the time you're ready to grognard you'd have a proud knowledge of the game's numbers....while still retaining that element of mystery that encourages players to theorise with each other about rare or undiscovered mechanics.
It seems like WL2 is deliberately hearking back to that - I hope so, as by providing a post-1990s-friendly ability to look at the numbers, while keeping just a few things hidden under the hood, would fit right in with their aim of making a 'new' Wasteland in the vein of what those games might have looked like if they persisted to the present day.
Anyway, back on topic.
Cha is seriously underated (I'm excluding SJ, as that's more a 'challenge play' than just a more difficult version of the base game). It just needs to be combined with a cha who can get the most out of it (i.e. no less than 3 use-often skills). With the bonus from demolitions, field medic and lockpick, he'll shoot ahead in level.
Anyway, there's two types of stats in the game - those that determine how strong your characters begin the game: Co, Str, Spd and Aw; and those that determine how much you'll improve (other than gear): Int, Cha and Luck.
A ranger squad should be taking both those things into account - enough of the former to survive the 1st half, and enough of the latter to ensure you thrive as the game goes on. There's simply no business comparing the benefit of Cha against any of the 1st 4, other than as part of that general tradeoff - they serve utterly different roles.
The underpowered stats are Co for the 1st group and Luck for the 2nd, while Spd and Int are the most powerful. Cha is as useful to that 2nd group as Aw or Str - you probably won't max it, except maybe on a deliberately extreme character build, but if you want a character to backload his power curve (and you will want at least 1, maybe 2 - a party full of front-loaded stats like Spd and Awa will blitz early, but eventually the enemies will catch up), Cha will factor in there somewhere.