Why do I have to wait 22 fucking minutes to finally get my two star Kassadin to complete the Void , and 24 mins for my two star Pyke to complete assasins
The answer to that is "you don't". You aren't supposed to force a comp you can't find like that. The skill part of the game is pivoting to what you do find, and making it work for you. Yes, it's a game based on mostly random factors. However, your goal is to mitigate those factors and utilize what is presented to you in the most effective way you can.
Yes, sometimes you will be absolutely screwed by the RNG while someone else is handed 1st place on a silver platter. However, top 4 spots (unless your MMR is too low for you rank) are all wins, and you are aiming for getting there more often than not, as opposed to aiming to get 1st or 2nd every game.
Also, I'd say that rank 3 units are overrated, but most players realize they are usually not worth the gold investment.