That is trueish, but the point of introducing a distinction between relative facts (before and after) and absolute facts (past and future) is to get a handle in change/becoming,

This is the stated motivation, although I must confess I have no idea how the A-theory is supposed to be even a partial explanation of becoming.

Note also that presentism is not exactly equivalent to A series.

This is true, but I don't think I conflated the two in my post. I didn't say anything about the existence/non-existence of past and future entities or space-time locations. I was talking about the A-theory, not about presentism, although the two are regularly treated as a package deal in contemporary metaphysics.

I actually think the presentism/eternalism distinction is more likely susceptible to shminux's charge of vacuity than the A-theory/B-theory distinction.