the "charisma" stat is the tanking stat
I'd suggest that it actually isn't.
Your only relevant tanking factor is the class, really. Because that's what ultimately defines HP, stamina and defense indexes per level.
Even min maxing his stats at character creation will not give any non-fighter lad the fighter's innate efficiency at tanking. Which is unmatched.
Then again, you have a couple of funny options in this regard, including wizards, who make for surprisingly competent frontliners.
As long as you heavily specialise them and reach a sufficient level and gear to do so (because, again, their class defines they default HP, stamina and defense indexes, and they're very low by design).
In such a case, for instance, intellect becomes the actual tanking stat, as it's necessary to ensure your buffs stay on for the whole fight (which, in most cases, isn't a problem anyway).
Dexterity, however, and despite being the regular wizard's most important stat, becomes practically a dump stat.
Keep in mind this is a rare exception.
Most classes in PoE define a character much more than any stat distribution you can come up with.