What is going on with the ranking system?

The ranking system really makes me feel bad. Every time I choose to play the place I want, the system give me the second one, and the teammate playing the place I want always getting reck by his opponent. Or sometimes I duo with my friend, he choose bot and I choose sup, he get other place but not sup. I hope the system cancel the secondary choose, which make some of the people can't play the place he/she want.[zombie-brand-mindblown]