The main problems with your system stem from how easy it is to abuse. If you can gain lp without winning then suddenly the focus becomes "What can I do to increase my stats" rather than "what can I do to win the game". This would be terrible and would only worsen a community that already struggles with toxic people.
Now here is the essay I ended up writing on why judging individual players would be very very difficult.
Creating an accurate system to score each player individually would be nearly impossible and saying that isn't nearly as much of an exaggeration as you might think it is. Riot would have to create what would most likely be the longest and most complicated piece of code ever written in order to make it accurately measure every play
For example you place a ward in dragon pit. Do you get points or lose points?
This seems obvious. Why would it be bad to have dragon warded? Well, here are a list of questions you have to ask to truly know if that was a good ward.
1. Where in the pit is the ward.
You may have placed the ward in the back of dragon pit, meaning it gets you less vision of the river, but it is also less likely to get swept or found by a pink depending on where it is.
2. Was the ward just to check over the wall to see if they are getting Dragon?
If the ward is just to avoid facechecking, is it worth any less than a regular ward, placed for vision? It may keep you from walking into a bad situation, or let you get the timer, but it could also just end up being a waste of a ward.
3. Will Dragon spawn within the time the ward is placed?
Clearly placing a sight ward that will just fade away because dragon doesn't spawn for 3 mins is a waste, but if you didn't have the timer you may not have known that.
4. What role are you playing?
Typically it's either the support or junger who keeps dragon warded. However is your ward worth any less if you are the mid laner or adc? What if you are the top laner and you walked all the way down from top lane just to place a ward?
5. What was your team doing while you warded?
For example your team was grouping top and pushing for the inhib while you were warding, and loses a teamfight because you were not there. Or what if your team was grouping for drag? Maybe a teamfight had just ended and you were placing the ward before you backed.
6. Did anyone find your ward?
If someone got extra gold because the found and killed your ward that helps their team, but how does it affect your score? Maybe you placed it in a rarely swept spot and they just got lucky or misclicked. Maybe your ward was in the obvious place, but your team needed that spot warded.
7. What happened while you warded?
You could have missed farm or gotten killed while warding. Maybe you went to ward as a support and your adc got hit by a blitz hook and died.
This is a quick list of different things to take into account even when all you did was place a ward in a specific spot. As you can see each of these questions also generated several more specific questions to go along with it. Now imagine you multiply this for every spot on the map you can ward. Some of those spots would have more questions to ask, some would have less. In the end though there would be a huge amount of programming to be done, simply to cover warding. You would have to do even more do calculate every aspect of a teamfight.
Now you should clearly see that creating an accurate system that can thoroughly evaluate every aspect of a game would be ridiculous to attempt. Not only because of the incredible amount of time and resources that would need to be spent to develop this program, but also because of the godlike computer system needed to maintain it. Riot would need to have a system of servers running an unimaginably complex piece of code for every single player playing a ranked game all at the same time, for every single action they make. The data storage needed would also have to be gigantic.
You may be asking, "Why can't they just do something simpler than this piece of god-code?" The answer to that: expoitability. If the code isn't this complex then it would be too easy to exploit. For example if every ward a player placed gave that player 0.01 points, then people would just buy sightstone and sit in base for 20 minutes spamming wards. Even if you make it so that only well placed wards give you those points, then people will just race to the areas which give more points to try and place wards before anyone else can. It needs to be this complex to get rid of the potential for exploitation.
TLDR:
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Riot needs to make the most complex piece of code in the world to accurately judge everyone's individual performance.
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If they don't people can just exploit it.
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They would also need a god-computer to run that code.
