In comp games, heroes aren't really built to be healers. Taric is an aura bitch, and Soraka has far more utility than her Q. She buffs single target armor, grants earlygame mana, silences, a great aoe with magic resist debuffs. Only her ult makes her more healery.
If you look at DotA, they mostly kept this theme. Dazzle and Omni for example: neither was a healer, but a hybrid that filled many roles at once. This is simply because straight out heroes are borrrring :P
And yes, Kayle can heal. Her W skill gives 10% bonus movespeed and a minor heal. At various times its interacted with Vengeance, but I don't think it has any correlation atm. I can't say with certainty though
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Shaco crits just fine with Sheen and Trinity Force: just keep in mind that THEIR damage is not amplified by his skill (they don't crit).
And yes...Shaco receives EVERY item effect. Its gross. His boxes were nerfed hard because of nests. Shaco players would hide 6 stacks of them, then lure opponents into them for absolute wtfkerpwn rape. And if they were in brush, there was nothing you could do about them.
I personally agree they need a minor survivability buff.