The age old question of what makes a player good is a hard one to define. The only way we have to judge is based off of the stats we can see about our play through the game. Which in some cases, the stats are a bit skewed or non intentionally false. When you have a game that logs hours played, but it bases that stats off the counting the amount of time the game was running. This can trigger a false stat, by counting the time, just from having the game running. I could leave the game running without playing it in the background for hours on end. It would still count this as play time. Which would give me a longer time played than I actually have. This could in turn make it look like I have a lot of experience playing this game. Say for instance 80 hours. Yet it was running without me actually playing it for 60 of those hours. This would mean I really only have 20 hours of experience. Other players might think your "skill" level is higher than it is.
This can lead to players thinking you are bad at the game. The whole you have played for so long but you skill level is low, you suck. The opposite happens as well, this is done through farming a stat. I remember coming across it in games like Battlefield 2. Players would ask to get X kills with a pistol so that they can earn a badge. This would make it seem like they are good with a pistol and got the required number of kills for the badge. When in reality, they had to ask for it, because they could not earn it themselves. The same happens in Overwatch. The boop from Lucio off the ledge achievement thing. Most players have to ask for it, sadly.
Stats are the best option to figure this out. You can assume the players skill from the stats, so long as those stats are not skewed or counted in a way that isn't a true form of counting it. Once you have the stats, you have to break them down to see which stats are most game changing or have the biggest impact on the game. Some stats are more important than others as well. Just like in sports. Yet the goal is to score, but also the goal is to stop them from scoring. So if you have a player with low points, that doesn't make them bad, if they lead the league in blocks and steals. Different players for different roles.
Some games have more roles than others. WoW has dps players and tanks. Dps and tanks are both needed. They work in unison or tandem. One takes the damage while the other dishes it out. In FPS games, some players are good because they can hide and camp well. This allows them to have a good kill to death ratio. Other players can have good kill to death ratios because of how aggressive they are. Some players are better with certain items than others as well. I remember in BF2 I was a beast with the rocket launcher. I could even get it to curve around buildings or curve it to my enemies. They said it was cheating, but it was pure skill from practice. I didn't see many players that could do it as well as I could. Since my skill level was high with this, it made my stats look amazing with it. Since I could secure kills with it easier than most players of the game. My stats on this weapon was at top of the charts.
Skill is based from so many factors in a game. Each skill has a role in the game. Some people are better at dodging, which allows them to not get hit as much. Which means they require less self healing in the long term, so the stat for that should be low for them. While other players use it so much because they suck and get hit a lot. So it would look like that player is better at self healing than the guy with a low amount. Which isn't true, he just didn't need it because his skill was higher in a different area.
Experience/knowledge of the game, the skills of actions within the game, and stats are all factors you must include. To base a player from any one area wouldn't be sufficient to make a good well defined "What makes a player good". A player can be the best at shooting and killing. Their aim is the best. Yet that player might lack map awareness, how to combo attack with their team or even just be bad at looting or controlling their person.
So what makes a player good you say? It is a toss up. Each game is different, each play style is different. Each player has their pros and cons. NO player is perfect by any means. Some are just better at executing the action better is all.