this is stupid since soraka has to build health items to able to stay healthy late game
your first point about her Q being a crappy heal for herself, well that is her "balance" that crappy heal makes her balanced because if she had a strong heal she would either be free win or perma banned, her Q's are ez to land if you know how to play her, tip is to Q whilst the enemy is in an action that they cant move it, example would be an auto attack
and your second point about tank warmogs, remember if you are a tank you need 2 things, health and resistance, so building warmog is not as op as you think, even though she has a bunch of health, she wont have any armour or magic resist so that health gets malted fast, but if she builds health and resistances then she doesn't have the support aspect of her champion and she loses the bonus healing affects thats she gets from support items making her heals weaker
so its either she has strong heals and gets bursted easier or weak heals and lives longer, and her Q gibes enough health for her to sustain but not too much that she can heal any mistake that she does, sounds balanced to me