As a support main, who liked Sorakas old kit I think I can answer some of those questions.
Why wasn't soraka's rework just put on a new champ so her current kit won't be broken and lost to the game?
The "old kit" already was a new one. It turned her from a walking Flask into an AP bruiser, which was an improvement, but one in the wrong direction. It is great playing her as a battle mage, but it's difficult playing her as the support healer she is supposed to be.
Why are the soraka fans who liked her old kit wrong
Not sure that even applies, the new kit is based on the old one and not that different.
Q is still an AoE damage, but ranged instead of PB. Hitting it still improves your heal.
W is still a heal, but a lot stronger one.
E is still a silence, just a bigger one.
R is pretty much the same as it was.
Why are the people who liked the mana gift wrong?
They weren't, not at all. Even Vesh says he wants to keep it, he just has trouble fitting it in.
**Why are the people who wanted her tanky wrong? **
You mostly build her tanky to get your close range MR shred in (AP bruiser style) They couldn't buff her heal while still having her tanky. It would make the Team nearly immortal.
**Why are people who wanted a battlemage who can heal others a little wrong? **
There are other battlemage healers, Kayle for example, but no real main healer.
Why are people who wanted a diverse role champ like she was wrong?
Diverse Role champs aren't wrong (mentioning Kayle again) it's just that they are difficult to handle, Keeping them viable in one role while not making them too strong in another (Alistar)
Right now there are already several people (me included) who think the new Soraka could make a good and decidely different jungler.