State A => State B multicycle path?

I'm afraid your reasoning is incorrect.

What you're discussing is the path between Launch_FF and Latch_FF.

Not the path between Latch_FF and whatever comes next.

Thus, in this context, you cannot afford to have Latch_FF go metastable even for one clock.

Also, metastability is not ensured to last just one clock...

That said, although your reasoning is incorrect, your usage looks mostly correct.

IF the logic guarantees that transitions in Launch_FF's output happen 2 clocks before being captured by Latch_FF, then you can use a multicycle factor of 2.

The little mistake you had is that, in this type of application, if the -setup multiplier is N, then -hold muliplier is N-1. 2 and 1 in your case.