Then Poland will reap enormous prestige from it.
No.
Orban explained well, why Ukraine in the EU is bad for Hungary.
It will absorb all the money, that would otherwise be going to you. It will make you poorer and less significant.
Ukraine has a demographic and industrial weight which Hungary and Poland do not possess. It would crush your agricultural, coal, and steelmaking industries. It would suppress the salaries of your people - because they are willing to work for less.
That's Ukraine.
Now imagine if Russia joins the EU? Nobody would ever remember about Poland again in Brussels? Even France and Germany would be competing to stay relevant. Russia, like Alexander I after the Napoleonic Wars, would seek to impose a dictate on how all of Europe should live. Russia's arguments would be infinite energy and the military power to ignore China and America.
For a Poland, that is climbing the ladder of the EU hierarchy, letting in a Russian monsters into the arena would not be good.