Well I really don't have any strong feelings about this. In fact, I wouldn't be bothered by the idea of leaving the hit rate completely out of the ranking. When I introduced the hit rate, I didn't expect that players would strive for 100%. I just thought it would give an indication of how much each player relied on sheer guesswork. (That is, a player with 20% hit rate is obviously playing a different game from someone with 80% hit rate.) So I still think the hit rate should be shown on the Challenge scoreboard.
But if the rosette is part of the ranking system, might there be occasions when a player feels hard done by if it turns out the common word they didn't get is not so common after all? Also, if two players have the same number of words in total, but player A has more common words, it follows that player B must have more rare words. Player B could argue they should be rewarded for having more rare words, rather than penalised!