“UKR and RUS overlap by around 60% to 80% mutual comprehension”
My limited understanding is they are about as close as Italian and Spanish.
I’m trying to learn Russian, but I am not having much success.
Actually closer - the "Russian" language is the East Slavic dialect from Muscowy v/s "Ukrainian" being the East Slavic dialect from the Hetmanate
They only split around 1300 AD. That's in contrast to Italian (Turin dialect) v/s Spanish (Castilian) that separated 700 AD