Same here, I'm a solo laner and I spend all my practice time last-hitting under turret and fighting people 1v1 / 1v2. I'm not a good jungler or a good adc or a good support at all.
I really am bad at bot lane especially because I'm very unused to playing with someone else in the lane against 2 other people during laning phase. I always misread my support and end up taking poke or using an ability on the wave when they are trying to go in for a fight.
I can kind of jungle... I know the IDEA behind how to jungle, I just don't have the execution down, and most of the jungle champions don't really fit with my personal playstyle.
I could practice them all and be average at them all I guess, but the only way I can have a high impact on games and feel like I'm contributing to the win instead of just "not feeding," is by playing my main roles (mid > top). I have a much higher winrate in those 2 lanes than any other by a large margin.