On a completely random note, I love how absolutely broken the implementation of the Alchemist's Grenadier Archetype is in PF:K. In the tabletop, you get sorta the same benefits, but you lose Brew Potion, a potentially defining Feat of the class, and you lose Swift Poisoning, which isn't a terrible class feature if you like to use poisons a lot, and is arguably in about equal value to Alchemical Weapon, which can be argued as being of pretty much the same "type" of class feature (i.e. weapon-enhancing). You also gain proficiency in
one martial weapon, and you lose poison resistance and poison immunity; arguably very small benefit and very small losses depending on campaign.
But in PF:K, you gain Alchemical Weapon, you get full Martial Weapons proficiencies, you gain the Precision Bombs Discovery on lvl 2 for free (which is practically a mandatory Discovery for all bombers anyway), you gain Directed Blast and Staggering Blast, to boot, later, and you lose... not Brew Potion, because there is none, and no Swift Poisoning, because there are none, but
one stage of Poison Resistance, and later your Poison Immunity, both which are largely useless anyway, because poisons are not tremendously common, and it's even less common that a backseat Alchemist would be struck by them.
Grenadier is almost entirely - to the point where the drawbacks doesn't even need discussing - an upgrade of the regular Alchemist. The same almost goes for the Chiurgeon as well, although it's much less pronounced (the benefits are not as big, and they actually lose
all their Poison Resistance).
Why on Earth would anyone play a regular Alchemist in PF:K? Or is something missing from the descriptions? Does Grenadier gain less Extracts, or something?
So if I go for a Divine Guardian to Stalwart Defender build, would lowering Charisma to 12-14 be alright given the circumstantial nature of smite and the lack of Paladin spells?
Depends on what you put those points in, now doesn't it? But yeah, I see nothing wrong with going for 14 Charisma in a Stalwart Defender build. I wouldn't lower it further, though, because remember that Charisma gives you a bonus to your Saves, which is something you'll want high as a Stalwart Defender - it's those Save-or-Suck spells that'll really ruin your day, not the heavy hitters. I've had so many encounters absolutely wrecked by fear effects.