My major problem I guess is thematically. Why are these spells legendary? Legendary minions are legendary because they represent specific, unique characters from Warcraft lore. These spells are just high-cost and powerful, but being high-cost and powerful has nothing to do with being legendary. There are plenty of high-cost and powerful common minions and plenty of low-cost and weak legendary minions.
If you're going to make Legendary spells, I think they should represent specific, unique things from Warcraft lore. Remember, the definition of "spell" is pretty broad in Hearthstone, so you could theme these legendary spells after particular events in Warcraft history or after specific, unique locations in the Warcraft world. For example, maybe instead of "Winds of Al'Akir", which comes across like Fist of Jaraxxus or Echo of Medivh, it should be "Throne of the Four Winds", which is a unique place.
Honestly I think your ideas are a bit plain. Maybe I'm not getting something, but why would it matter that health is going to be changed to 1 if they're going to be indestructible? I mean, inner rage (assuming that for some reason a paladin would have it) would still work as a buff, right?
I think that to qualify spell as legendary, it should be something like Skull of Gul'dan etc.
Also likely to be balanced so that there's a good reason why you don't want to players have more than one under normal circumstances. Not required but would further boost their status as "legendary" spells.
Some legendary cards are often played in the ranked mode because they either are just that powerful to warrant their include in a deck, they have synergy with a deck that makes them worthwhile or they have some kind of potentially powerful gimmick.
With spells, making them simply better to warrant their legendary status doesn't really work that well.