KDA is an important value that easily show the level of a player. Another value would be your MPM and such.
That being said, there is a "muh KDA" mentality coming from trash games like CoD and the like where K is the only thing that matter, and then there is KDA, where K, D and A all matter.
If you check proper Gold and above players, you will rarely see them with "bad KDAs". Sure you'll see plenty of people with negative KDAs, but they are very often tied to their playstyle or role (Gold+ is when people can truly start to main thanks to the lower amount of players, this will probably slide to Platinum next season seeing the recent percentages).
As a general rule, if you have above 4 in D, you're not Plat + material. K and A are so much role dependent, it's impossible to give a number, same for MPM, but it should be the closest to 10 possible (and should be at least 8+ for a top/mid/marksman starting Gold).
A fault I have when I'm super fed is I get ballsy as ***, and I'll expend everything to pick off somebody I find in the jungle alone only to have their whole team jump on me while I'm doing it :(
I noticed that coincidentally with my better results, I started to notice when I have this vision and was able to stop myself much sooner than before. To the point where I'm way too cautious sometimes, though. But it's good when you become faster to gauge what you can and cannot do given a specific situation.