So, you're saying RIOT doesn't want us to play as carries or support.
That's basically what it seems like.
All the successful support characters have built-in escape or tank abilities. Alistar is a tank. Janna has a shield and incredible escape ability. Taric is very tanky. Sona has heal, speed, and defense boosts. They also all have great crowd control and do decent damage. Alistar has two abilities with 1-1 AP ratio FFS. Basically, none of them are pure support. Soraka is. She does almost no damage, doesn't tank well, uses up her mana super fast, and only a silence for real self-defense... but she has two (weak) heals... making her basically pure support... and I haven't seen an effective Soraka in-game in months. I hear stories, but I never see it.
Carries (mostly ranged) are all worthless unless guarded by their teams like precious jewels. They're very item-dependent and require large investment before they become effective. Tanks, assassins, and nukes all have abilities that allow them to do initially greater damage and catch or escape nearly at will. Basically until you've built 3 or 4 items, playing a ranged carry is like walking a tightrope on a windy day over a lavapit. You step one pixel out of bounds and you die. It only gets better if you manage to farm better than your opponents, and the only thing they naturally have going for them is they tend to farm more effectively, thus allowing this to happen once in a while.
I often play Teemo, Ash, Caitlyn, and Tristana. When I play these, it feels like more of a support role than when I'm playing actual support characters. I seems like my job is to be a whittle away at the enemy like a general nuisance, plant mushrooms, and slow with ice/frozen mallet to set my teammates up for kills. Then I play someone like Mundo, Mord, etc and can destroy those same characters in seconds, and easily escape most of the time if something doesn't go as planned. With Mundo, all I need is Warmogs/Spirit Visage/Phantom Dancer, and I can solo any hard DPS in the game most of the time so long as they're not overfed... with just one attack item.
I just don't understand Riot's approach to balancing. It's fucking alien to me. They make so little sense.