I think the issue is not people playing this game for different reasons but complaining about this game for being a story-driven MMO and locking content out behind it. Like, it's a Final Fantasy game and they take a different development course compared to other MMOs or so they try. This idea of locking out content behind the expansion is nothing new at all. People are free to skip every cs and finish the MSQ in no time. I wouldn't care, it's their choice. But if you don't like the story, that's up to you, now asking the dev team to remove the condition of finishing the main story because you (And I don't mean specially "you") don't like it or you think it's tedious, it's a different thing.
Heck, it's not like they don't receive anything by doing the MSQ post Praetorium! Maybe it's not a smooth transition but we don't even know if the MSQ quests will be adjusted to give experience as well! They also unlock several trials and dungeons that will be still useful post 50. The new guys will complain if they need to. No need to be a white knight for a thing that we don't know if it will be an issue. It's silly. Now it brings me back memories... I remember didn't like to level up a different class in WoW when WotLK was out because I was unable to create a Death Knight if I didn't have a level 50+ character... but you know what? the reward for all these efforts was to play the class I liked. Ya, I didn't like it back then, but that was the dev's team decision and I learned to respect that. If people want to act like an spoiled kid because they didn't get the job they wanted as they started this game, I'm so sorry...
Finally, all the content behind the Ishgard gates are intended for level 50+ characters. Even the most lame monster will one-shot you if you go with a lowbie. Even Yoshi-p said the expansion will hold more "world danger", so all the previous content comes in preparation for that.