My point is that, while there isn't a single universally defined future, for every observer there exist events that haven't happened yet, and no observer is ever going to communicate with some other observer and disagree about whether an event has happened yet or not. They can only disagree about the order in which events in their shared past happened.
Additionally, there are events that are in the future for any observer in any reference frame anywhere in the universe (except for those already caught beyond the event horizon of a black hole, but their future consists exclusively of the black hole so it's not that interesting to the discussion). For a simple example, present day on Earth was in the future for any observer anywhere in the universe 5 seconds after the big bang, regardless of their speed. So, there is no reason to say that present day Earth must have already existed 5 seconds after the Big Bang.
Of course, the block universe model is self-consistent, so it's possible it's correct. All I'm claiming is that an evolving universe is also consistent with relativity, though the way it evolves is more complex than a single universal arrow of time.
Additionally, there are events that are in the future for any observer in any reference frame anywhere in the universe (except for those already caught beyond the event horizon of a black hole, but their future consists exclusively of the black hole so it's not that interesting to the discussion). For a simple example, present day on Earth was in the future for any observer anywhere in the universe 5 seconds after the big bang, regardless of their speed. So, there is no reason to say that present day Earth must have already existed 5 seconds after the Big Bang.
Of course, the block universe model is self-consistent, so it's possible it's correct. All I'm claiming is that an evolving universe is also consistent with relativity, though the way it evolves is more complex than a single universal arrow of time.