Squire, you cannot agree with the former and disagree with the latter.
Afraid I can.
Let me break it down for you: "Simultaneity is relative" means that simultaneity depends on relative motion of the observers.
It does not specify exactly what that relation is (though Einstein does, in explicit mathematical detail). But just semantically speaking, all the statement "Simultaneity is relative" says is that IT IS POSSIBLE for two observers to disagree on simultaneity.
It most certainly does not imply that ALL observers disagree.
How about this statement, about perspective: "The apparent size of two objects varies relative to where you stand."
Does that imply that no two people will agree on the apparent size of two objects? Maybe you think it does.
Now, what the mathematical description of relativity of simultaneity says, is that there is a mathematical relationship between simultaneity and relative velocity.
Mathematical curves, I hope you realize, can go through zero. This one does. It goes through zero when relative motion is zero. It also goes through zero when spatial separation is zero.
What that means is that:
(1) Two observers who are not in relative motion will agree on the simultaneity of events in their reference frame, and
(2) When two events which occur at the same location, ALL observers will agree on their temporal relationship. If one observer says they're simultaneous, all do.
If simultaneity is relative then there is no way for 2+ observers to establish an exact moment of time.
There are precise procedures defined by Einstein to establish an exact moment of time. Further, simultaneity is not "relative" between two observers who are non-moving with respect to each other.
If we cannot agree as to the simultaneity of an event
If we are not in relative motion, we certainly can.
then we cannot agree when 'now' is.
It becomes trickier to define "now" when things are in relative motion. But not impossible.
If there is no absolute simultaneity, then there is no absolute now.
If there is no absolute now, then there is no universal now.
If there is no universal now, then there is no universe.
Now you're doing the woo-woo thing of taking a statement you think Einstein said, ignoring the actual mathematics you didn't understand, and spinning off into semantic la-la land. It's exactly like the people who take the Heisenberg Uncertainty Principle, a precise mathematical statement about certain pairs of variables, and turn it into "Heisenberg says nothing can be known for certain."