[RPG] n official Pathfinder “Mana” system for wizards

The biggest reason I can think of is that Dex, along with Wisdom, is already at least on the border of being "too versatile," in the context of 3.5 and Pathfinder. While it's true that Rogue, for example, is a weak class in the core rules, it isn't due to the reliance on Dexterity.

In 3.5e and PF, Dexterity does these things:

• Determines your initiative. This ensures that Dexterity is at least marginally useful for every class in the entire game.
• Adds to your armor class, and more importantly, boosts your touch AC. Also good for everyone.
• Determines your to-hit with ranged weapons and finesse weapons.
• Determines your reflex save -- another one that's a little important for everyone, since the most common thing that invokes a reflex save is either a trap or an AoE attack, which everyone in the game is likely to be subject to at some point.
• Is the modifying attribute for a proportionally large number of skills relative to other attributes

This is also pretty much identical to the way that 5e handles Dexterity. So why does it work in 5e and not 3.5e and PF? There are some key differences:

• In 5e, touch AC is not a thing. This is important.
• Armor now has a strength requirement on it as you go heavier, as well as being much stricter about limiting Dex bonus to AC, meaning it's either impractical or pointless for most characters to stack a high Dex modifier with something like mithral full plate; heavy armors with improved Dex-to-AC bonuses.
• In 5e, modifiers aren't really a thing outside of your regular old Str/Dex + Proficiency bonus to attack. Magic items are also supposed to be harder to come by, although that can vary with your GM. Depending on whether you can get advantage or not, this might make it harder for you to accumulate the modifiers you want (advantage is supposed to be equivalent to about a +4 or +5 bonus, if I recall correctly)

In conclusion, it's clear that giving Dex the same functions as 5e would make it more powerful in the context of the rest of the rules in PF. I can't say for sure that it would break your game, since that mostly depends on what class the character in question ends up being. Balance in PF depends highly on the individual class.