How was Alexanders army able to deal with the Persian archers?

[Flavius Merobaudes]

The Romans were at war with "Persians" (or their successors, like the Parthians) for around 5 centuries on and off... You can see the outcomes, you don't need to imagine. The information is there.

Forgive me being so honest, but that is totally incomparable to what we are talking about - at least if I understood seleucid empire's question correctly.

We were talking about what might have been if the Achaemenid Persians would have faced the Roman Republic instead of an alliance of Greek poleis in an invasion. This was a one-sided and locally confined operation.
You try to compare it to the clash of two empires half a millenium later? Really? The Roman Empire was fundamentally different from the res publica of earlier times. This difference is even more evident between the Achaemenids and the Parthians. Just look at social and political structure, look at populations and economies, and therefore military capabilities. Look at advances in science and technology, and in case of the Parthians look at the ethnic change that took place - with all its consequences.
What you said is just as much BS as comparing the Roman Empire to today's Italy would be, or comparing the 13 colonies to the modern USA.

But I grant you that this is not really your fault but a widespread misconception. We humans like to attach items to certain categories, and we tend to emphazise similarities over differences. So there's no need to take this personal if I say that there is not a shred of truth in your comparison.