I see where your coming from where the reward of the story seems to be 'handed-out' but coming from another raider I don't think this is a fully fleshed-out idea, although I see your points.
First of, having the release of the Alexander raids being released at the next subsequent patch is way too time consuming and costly. For example, you stated '3.05: Release of Alex Savage Tier 1 (Gordias)' and '3.1: Release of Alex Normal Tier 1 (Gordias)'. That's 3.5 months of waiting just for a player to get involved on something they care about; the story.
Players should have to pay $42 over the span of 3 months and a half trying to get engage in the story because they are going to be a ostracized by players by 'not being good enough'. Its pretty hectic right now for most players who are doing their best to clear, even harder to be part of a party that's patient and is willing to commit.
Even though I don't agree with your idea, I'd say if they consider going that route to just make it the mid patch of the time an raid is released (i.e. 3.2: Release of Alex Savage Tier 2 (Midas) THEN 3.25: Release of Alex Normal Tier 2 (Midas) ). The majority (the casual players) needs will be served in a few, short weeks instead of having to wait and hard-core raid players would understand the mechanics well enough in getting into savage which also brings another point with one of your arguments.
"This won't "spoil" 70% of the mechanics for Savage". I would call Savage mode being a spoiler for Normal/Hard; it's a pace to which players who choose to go the route of Savage mode can know what they're prepared for and plan ahead of the game. Your statement would have more merit if normal was released first. Normal/Hard mode will be a joke and there will be no point in releasing it because the mechanics will be recycled with an element taken away from the fight.
Advantage #4 (gives the casual players who don't have time to dedicate multiple evenings per week to a static, a chance to see the story, just in a later patch) comes across shallow and callous to me. Having Normal/Hard being released the same as Savage would help said casual players gear up and prepare ahead if they choose to go that direction. Game design wise the FFXIV made a wiser choice in releasing the difficulty content the same time because it makes a better door for entry for those who may have never considered this. Take it away and it will drove off casual players (market wise is a majority of players) because they're being booting 3.5 months because they're 'not good enough' while a minority is being served.
We know this because there are some players still going through the story and trying different jobs; this being the perfect opportunity to hone and refine their understanding of the instance before they just jump into it (Alex Savage) without them knowing what they're in store for which I'm sure you wouldn't want too because you'll have a influx of inexperienced players in your group.
Not a smart move business-wise and mechanically for the game itself.