 The reason why it is worth introducing this bit of jargon is that once you present the relativity of simultaneity as the combination of claims (i) and (ii), you can also note that the motivation for claim (i) is importantly different from the motivation for claim (ii). The motivation for (i) is a series of empirical results at the end of the nineteenth and beginning of the twentieth century, including, most famously, the Michelson-Morley experiment. No one should deny this part of the relativity of simultaneity. The motivation for (ii), by contrast, is less often explicitly discussed, and seems to involve the commitment to some sort of general extra-empirical principle like “eliminate unobservable entities whenever possible”, or “eliminate excess spacetime structure whenever possible”. This means that presentists and other A-theorists have a way of avoiding the worry from relativity without any conflict with empirical results—they can reject whatever extra-empirical principle motivates (ii). Whether you think the costs associated with this move are worth paying will depend on your degree of commitment to the A-theory, what exactly you think of the relevant extra-empirical principle supporting (ii), and whether that principle plays an important role elsewhere in physics.