I agree the class could benefit with some class feats that reference charisma more. Thaumaturge's Investiture is a nice example of a feat that could be good and references charisma. I kinda wish that feat was earlier, perhaps switching one more activation with it and having one more activation work charisma times a day but only once per item.
I have never had a character who actually used up all of it's investiture but if there was an early feat chain that involved investiture maybe i would be willing to spend my money on cheap 1/day items.
Charisma is one of the most useful mental stats generally. It's selection of skill feats are some of the most powerful in the game.
My issue with that is how its mainly related to the "face" style things. (not only face of course but) Which not every character like this wants to be. I for one have little interest in ost of the charisma stuff.
As I am not a fan of most of the charisma related stuff but a huge fan of this class I would love more charisma related in class stuff for it. It would lessen the disappointment in having to invest in charisma for Find Flaw abd Class DC (as you cannot chose to not replace it with charisma).
So having more in the class related would lessen the pain for folks who have no interest in the charisma skills for their character concept.
though Im still a fan of letting int or cha be an option. It balances well with int or wis on the psychic. but thats here nor there.
The main problem of Charisma is the way as the 6 stats has build since the first versions of D&D. But after 3.0 when they ended the mostly worst save system I saw in a game the 6 stats was divided in:
STR: Melee hit and bonus damage, range damage and sometime throw hit
DEX: Range hit, Sometimes Melee hit, AC and Reflex Saves
CON: Additional HP per lvl + Fort Saves
INT: Some spellcaster CD + some spellslots + additional skills
WIS: Some spellcaster CD + some spellslots + will check
CHA: Some spellcaster CD + some spellslots
So since the beginning CHA was as a inferior status over the others. When the PF2 probably for a sake of tradition and to diminish a little the learning curve for old players and maybe to don't difficult too much some conversion the PF2 keeps the stats system from PF1/D&D3 and also add perception as a special skill that empowers even more the WIS. Sometime after only in GMG they show an alternative that merges CON with STR, dividing DEX into 2 stats and moving Will to CHA. This stats is not only would made the things more balance but putting will in CHA make the stats more flavorful but in the end is just an alternative suggestion. The Paizo don't had the necessary boldness to use this stats organization since the beginning.
That's why we have the CHA currently mechanically poor balanced and confused in flavor once the Will is WIS based instead of CHA