Act II on Rails? There's quite a lot of choices available and can affect the way the game plays out in Act II. The claim that Act I is a sandbox is just as confusing.
Try playing FFVXI for game that's on rails, gorgeous looking and I did enjoy it but the only choices you get is speccing your character's skills.
There are no random encounters, each area has a finite number of quests in a set number of locations. Once you've defeated or charmed your way through Act I there's no reason to stay there, you can't create a settlement, find more monsters to slay etc., if it was a sandbox that wouldn't be the case. The game's longevity will be players trying different builds and origin characters and choosing different paths in all 3 acts.
The Gale story line ties in with Forgotten Realms lore and I liked it, can't agree with any part of your post. The "what I see on Twitch" sounds like you haven't even played it yourself and explains why you think any of it is on rails or a sandbox.
