That was the mystery though, it was just part of the plot. Some fans made it into one, but they latch on to some details and then get disappointed when it isn’t something huge. The reveal makes perfect sense character wise and was executed perfectly on the show. You could really feel how it made both of them feel.
But I do try to temper my expectations, assuming the writers want the story arcs to make plausible sense in terms of character and plot developments. Some surprises are welcome, of course, but they have to have a grounding in what was presented up to the point of the revelations. For example the RA being Spock or Future Archer seems pretty implausible at this point. Young Michael making incestuous sexual/romantic advances on young Spock also seemed pretty farfetched as a theory as to what had caused the rift.