2. Infield singles and ground rule doubles are still singles and doubles.
3. The biggest point of any of my response to you has to do with the bolded phrase in your post. An infield single and a ground rule double have less impact because of runners on base.
Here's what the fangraphs primer on wOBA states:
So, while I don't disagree that infield singles and ground rule doubles are worth less than regular singles and doubles, what you're asking of the statistic is something the statistic itself was never designed to do.This stat is context-neutral, meaning it does not take into account if there were runners on base for a player’s hit or if it was a close game at the time.
wOBA is interested in what the batter has control over. Runners on base are deliberately ignored because a batter cannot control who and when other players are on base in front of him, same as a runner can't control what a hitter does behind him.
I really hope you're getting this. My point has never been that you're wrong about your assessment of the values of those events. My point is you're expecting wOBA to do something that goes against its stated purpose.
To further the point, I'm going to lay out scenarios for you.
Keep in mind that this is entirely hypothetical and only for illustrative purposes.
Player A hits 30 doubles and every single one of them is a ground rule double, but every time he bats there is a runner on second base, which means he has driven in 30 runs with his doubles.
Player B hits 30 doubles, none of which are ground rule doubles, but every single one of them is with nobody on base in front of him, meaning he didn't drive in a single run with his doubles.
Whose doubles were really more valuable? Player A, right? However, because wOBA doesn't concern itself with where and how many runners were on base for batting events, they are credited with the same amount of production.
A statistic that does what you're asking wOBA to do is WPA, which uses something called the Leverage Index to weight each event based on win probability changes. This statistic correctly weights things like ground rule doubles and infield singles.
So, please, for the love of God understand what I've been saying here. It's confusing at first, but I feel like I've laid this out in a relatively simple way that you should be able to get it.
And may I add that I think it's great that you are getting interested in advanced statistics. More fans should be. I'm not claiming to know more than the average person about them, either, but I definitely have had experience with looking at these statistics and the basics of how they're calculated and their purpose. Asking questions is great, but when you ask questions you have to be able to hear something you may not agree with and flesh it out without jamming your fingers in your ears and refusing to believe it.
No statistic is perfect, including wOBA. But, for what it does, it's a really effective tool to look at how a player has done. It's also effective at predicting future performance better than just about anything else out there.