In my humble opinion, for what its worth, no its not, its no more sexist than calling a man a man and a woman a woman.
Its as ridiculous as actresses wanting to be called actors, but wanting seperate categories for the two sexes when it comes to awards,if they want to be called actors then there should only be one category for actor,
Actress is no more sexist than any other female equivalent of a masculine noun.
For the most part, players are not interested in the names, nor the art work, they would work just as well with level numbers and type.
Nothing wrong with clanmates instead of clansmen.
I agree that there are a few things that should be changed with regard to player designations as this is a personal thing. There is something about the CvC announcement that always grates with me but I can't see it now. And I don't think the Northern Brotherhood is a good name for the new pay-for-quests item. I would prefer Message to Clan rather than Clanmates.
But I disagree with renaming Shieldmaiden and Horseman. These are not sexist words - Shieldmaiden is even from Norse mythology.