The Crimson Binome
Hero
One group prefers to make decisions as their character would, based on their understanding of how the world actually works. Role-Player.This is the crux of where our views diverge. There are at least two types of players here:
One prefers to have fun telling a story with friends and using the system to help them do that. Role-Player.
The other has fun manipulating the system to win a perceived competition with other players. War-Gamer.
The other makes up facts about how the world works, based on their own out-of-game notions about how they want it to work. Meta-Gamer.
Another group invents facts about how the world works, to facilitate a narrative that they want to promote. Story-Teller.
D&D is a role-playing game. All of my answers are from that perspective. Story-telling is entirely missing the point. Meta-gaming is anathema. Your mileage may vary.
Zero percent more effective, ninety-five percent of the time. Joe and Larry would have to be targeted by twenty Charm attempts before that bonus to Wisdom paid off one time, on average. (As a side note, I've played entire campaigns from one to twenty and barely made twenty Wisdom saves over the course of the whole thing.) It's also entirely within the realm of possibility that Larry would consistently succeed while Joe consistently failed. That small of a modifier is entirely overwhelmed by the randomness of the die.As a side note, how much more effective is Joe with his Wisdom that has not been dumped (and maybe even bumped up a little) when him and Larry are the victims of a Charm spell.
Now you're talking feats, which actually are comparable to increasing your primary stat. I would expect both Bob and Joe to consistently outshine Larry from level four until level six, because you've altered the relevant costs in order to make it so. Of course, Larry wouldn't actually take nothing at level 4 in the hopes of getting one feat-equivalent at level 6; in a world with feats, Larry would take Lucky or Resilient or something else which is actually as useful as +2 to Strength.Or, how much less damage will Bob take once he engages in melee because he was more effective than Larry at range. Then again, were Larry to be Charmed and turned against Joe or Bob, how much less effective would Larry be when Joe knocked him prone, or Bob proves his mastery of great weapons.
Don't confuse the player with the character. Larry may be a jerk, but Larry's player is just doing their best to play the character they envisioned. Ideally, the game should support playing all different types of characters, whether they are jerks or team-players or gruff lone-wolf types with a heart of gold.Larry's player would not be welcome for very long by the group that he tries to steal the spotlight from by proving his system mastery.
The underlying problem is that the game makes it more likely for certain character types to thrive, where others suffer and risk threat of death. If you want to play a fighter who is more of a scholarly type instead of a typical meat-head, for whatever reason, then the mechanics of the game actively punish you for it. Your house rule doesn't solve that problem. (A house rule that would solve that problem, for example, would be something like removing ability scores from the attack roll and replacing them with double proficiency; or letting you add your highest ability bonus to the attack roll, instead of just Strength or Dexterity. Those house rules have other problems, of course, but they would address the problem at hand.)