Not long ago I had a conversation with a linguistics professor from a renowned European University. He says there’s no big difference between Russian and Ukrainian languages. Basically Ukrainian is an archaic and rural version of Russian. That’s why it sounds a bit funny to a Russian ear. There’s even a joke: Any movie translated into Ukrainian automatically becomes a comedy. So there’s no wonder Russian speakers in the East of the Ukraine don’t want it to be imposed on them...
Your linguistics professor is wrong. The roots of Ukrainian are in the Czech language Ukraine was Christianized well before Russia. The similarities in alphabet and language arise from Russian taking from Ukraine culture