They were outstanding at wrestling. https://en.wikipedia.org/wiki/Wrestling_at_the_Summer_Olympics
the Soviet Union still leads the Olympic wrestling medal count.
I don't think they were great at any other combat sports though. They won a decent number of boxing medals, although nowhere near USA or Cuba levels. Olympic boxing isn't the best way to judge a country's boxing skill. Plenty of good American boxers skip the Olympics and go pro. Meanwhile, you've got Cubans who won three boxing medals because they couldn't turn pro and boxed in multiple Olympic games.