I feel like people who use the "time bubble" theory are taking it too broadly. Clearly there are events that have happened, and therefore time must unfold in that space. You can put things in a bubble or sort of suspend quests and locations to certain points in time, but you cannot assume that the events between ARR and Shadowbringers have only been a short amount of time.
What I like to do is separate the expansions into about a year's worth of "events." Which seems to be the most likely case. Maybe ARR was a short amount of time, but you cannot tell me that between the end of ARR and the end of Seventh Astral Era, that at least half a year hasn't gone by. This stuff takes time to set up. You think the Crystal Braves were set up in a day? A week? A month? Please, recruiting an army takes several months, at best. Even with Alphinaud tirelessly finding new members.
By my standing, about three years have passed since the introduction of ARR up until the end of Stormblood. That leaves plenty of space for your character to have done all the MSQ stuff and run through all the side quest, raid, and expeditionary(24-man) content. The way that the characters talk, they make it clear that we don't really use the aetheryte crystals all that much, if at all. Most content seems to be "walk" to this place, not "teleport."
If you really want to assume that an absurdly short amount of time or absolutely no time has passed between the events of ARR and Stormblood, I mean of course you are free to do so. And I'm not saying we should even follow the calendar events of the world. But honestly it's not a very interesting topic to just assume that everything is episodic or that everyone's stuck in a time bubble. That just makes it seem like no one can grow as characters, which they all clearly have.
The time bubble theory could be applied per expansion, where all events and side quests do go in a sequential order, the MSQ being the only thing you have to rigidly stick to in order to see events afterwards, but I don't think you could reasonably make an argument where both Gaius van Baelsar was both just defeated in the Praetorium and is also seeking to slay the Ascians while wandering through the Burn. The devs are busy actually making the game, leave them out of it, you should be able to make your own conclusions to how long the timeline is so far.