Incredible analysis from Lang focus:

Ukrainian “Lexical Similarity” with

Russian: 62%
Polish: 70%
Slovak: 66%
Belarusian: 84%

Russian vocabulary – from Lativ via Old Church Slavonic
Ukrainian vocabulary – Original vernacular slavic words

I think the last fact of vocabulary origin speaks to the socio-political difference that defines the two cultures: centralized and authoritarian vs individualistic and free