I definitely think WotC dropped the ball in not updating attributes for 5e. They've never been particularly well handled. Here are my biggest complaints in a nutshell:
1. They aren't very well balanced. Some attributes (Dex, Con) are much more generally useful than others (Int, Cha). This is in part due to the way the mental stats are caster-based (see below)
2. Dex is too broad relative to other scores. It really should be split into Dex and Agility, the same way Str and Con and Int and Wis are separated.
3. There is no ability score governing aptitude with magic. This is a personal preference, but IMO it makes no sense that, say, Int, governs literally everything about how proficient you are at casting spells, with no measure for innate ability outside of how smart you are. it also leads to Int being a dumpstat for every besides wizards, which is goofy.
4. The mental stats are all weirdly conceived, poorly defined, and aren't even utilized well within the poor definitions used. As an example - Wis is actually an aspect of Int, and has nothing to do with perception, and is inversely correlated with zeal.
So, here I present my ability score system designed for granularity (there is an option to come for reduced granularity, featuring 3-4 attributes instead of 6). This expands the 6 current scores into 9 (which scales neatly), with one of those 9 (Thaumaturgy) being used only for spellcasters. This is intended for two things - a.) to help balance spellcasters relative to non-spellcasters, and b.) to allow other attributes to be better balanced and desirable for all classes. All spellcasters will use Thaumaturgy to set save DCs and attack rolls for spells, but may use other attributes as well - such as a wizard receiving bonus spells based on Int. It's worth noting that virtually all classes will face increased MAD from these changes, which is actually intended. Character building should involve tough choices, which makes it more interesting and leads to greater diversity among characters. I am well aware that there will probably need to be tweaks to some class features to make sure none are unjustly boosted or nerfed by these changes. It will be a work in progress.
Strength - Muscle power and stamina. Attack Rolls - melee and thrown ranged Skill - Athletics. Secondary Mechanics - Encumbrance.
Dexterity - Hand-eye coordination and motor skills. Attack rolls - finesse melee and ranged. Skill - Legerdemain. Secondary Mechanics - Crit range.
Thaumaturgy - Aptitude for channeling magics. Attack rolls - all spells. Skill - Spellcraft. Secondary Mechanics - Rituals
Constitution - Endurance, health, and tolerance of discomfort. Skills - Focus, Tolerance. Secondary Mechanics - HP and HD
Agility - speed, physical reflexes, grace, and balance. Skills - Acrobatics, Stealth. Secondary mechanics - light/no armor AC, Initiative
Instinct - Awareness, mental reflexes, sensory processing - Skills - Perception, Survival. Secondary mechanics - passive perception
Intellect - education, memory, problem solving. Skills - Lore, Logic. Secondary mechanics - Tactics (variant Hero Points)
Wisdom - judgment, maturity, and empathy. Skills - Caregiving, Investigation. Secondary mechanics - Sanity (resource for mental damage)
Charisma - presence and magnetism. Skills - Influence, Performance. Secondary mechanics - Reknown and Loyalty (charisma also takes on more will based saves)
That's all! As you can see, all "primary attributes" (Str, Dex, and Tha) are tied to one type of attack/dmg roll and 1 skill. "Secondary" attributes (Con, Agi, Awa, Int, Wis, Cha) are all tied to two skills. All attributes have at least one sub-mechanic making them worthwhile for anyone who wants to take them. It's also worth noting that 4 attributes (Str, Con, Agi, Ins) are applicable to pretty much all ambulatory life forms while the other 4 (Dex, Int, Wis, Cha) are specific to intelligent life.
