Oda is not going to keep something just because you don't want them to change.
There's nothing wrong with Cat Burglar or King of Snipers, names that Oda himself came up with and has been using since 2007. Why would those be changed in the first place?
I mean, those epithet's have been up for 2 years already. They've had plenty of time to be stuck on people's heads (both in-universe and in real life).
Brook was never known to be a Straw Hat before the timeskip and was generally unknown so he justifiably gets a new one in-universe.
Heck, the whole point of epithets is to give a memorable way to refer to someone. They can range from badass titles to embarassing nicknames. Expecting people to just refer to somebody else in a new way is very hard to do.
Oh, and people can have more than one epithet too, so whatever.