DND_Reborn
The High Aldwin
One archetype that D&D handles poorly is the fighter who has "moderate" Strength AND Dexterity. (The mechanics really reward you for picking only one of Str and Dex and pumping it into the stratosphere, while dumping the other.) So I've always wondered if Versatile Style could be for them. For example,
Expert Style: When you make a melee attack with a versatile weapon you are wielding in both hands, you may add double your proficiency bonus to an attack roll. If you do so, then don't add your ability modifier to the attack roll unless it's negative, and add both your Strength and Dexterity modifiers to the damage roll.
...That's kind of a mouthful, but the net is that your total attack bonus lags slightly behind a maxed-out point-buy character until 17th level when it reaches +12 (the normal character would only have +11 at that point). But it's only slightly behind. And your damage potential could be enormous (if you are maxing both Str and Dex), typical (if you have a moderate Str and Dex), or poor (if you actually have a terrible Str and Dex: that's now an option, too).
All of those scenarios seem like good trade-offs; pumping both scores is costly, while dumping both can get you great scores elsewhere. In fact, the only people this style really doesn't benefit is someone with the typical ability modifier progression of +3/+4/+5 at 1st/4th/8th levels.
That is a good point, that a "balanced" STR/DEX fighter doesn't benefit compared to the maxed out STR or DEX one.
One idea I had was doing something similar so a character could add both STR and DEX mod to attack rolls, and then base damage depending on the weapon (finesse = DEX, others = STR). Maybe a versatile weapon could allow the wielder to do that.
I also find it interesting that you think the typical ability modifier progression bumps at 4th and 8th levels. Sure if you don't play with feats, but I have yet to see a player select the ASI over a feat twice in a row. We normally don't see the first ability score bump until 8th and then another maybe at 16th.