commie
The Last Marxist
I am C1-fluent in both Polish and Russian. I'd say that they are much more similar to each other than, say, German and Dutch. Or French and Spanish.
I feel the same though statistically it seems there are less words in common between Polish and Russian than German and Dutch for example. I never really understood this unless there's a bunch of old Slavonic words counted that neither country uses daily which skews the stats. I for one can easily work out the bulk of a Russian speech and their issue with Polish tends to be more based on the speed of talking(just like written Russian is an extra hurdle for me due to first transcribing the Cyrillic into Latin script in my brain, before translating. I'm sure as I get better it will be automatic and I'll 'see' Cyrillic as natural).
I prefer Russian to Polish, less 'sz' and 'cz' sounds that assault the ears.