Yes, the key word was competent. At least, when almost all of the roles were all called up, or you're the last pick, at least suck it up and have a mind of taking up the responsibility given to you, whether you like it or not.
You don't have to know every role but you should know more than one, especially jungler OR support. You have to know one of those roles or you will constantly have problems in queue if you are low in pick order. Being able to play 3 roles is probably ideal and if you do get forced into a role you know you are terrible at, then suck it up and queue dodge unless you want to lose elo.