Yeah, in ranked you really need to play to your two strongest roles. I found out the hard way whenever I used to play ranked and do support/fill because 99/100 times I would get support. Of course, the one time that I don't get support, I get jungle, which is my absolute worst role to the point where I don't even understand the mechanics of it, what to buy, etc.
I also think that it's harder for supports to be able to get just one other role down though, because of the lack of people picking support. For instance, if you wanted to practice your midlaning in a normal and queue support and mid, guess what you're going to get most of the time? The only way I could see to alleviate that would be to pick a third role like top or mid. I tend to give other support mains flack for wanting to be babied too much, but I feel that this is a legitimate gripe with how dynamic queue works specifically for support mains.