Inhumans will? Or X-Men will seem like a rip off of X-Men? I'm not following.
Personally I don't think Inhumans and X-Men are similar enough for any significant amount of people to completely turn the other away. Inhumans are already out on the small screen and comics and then films like Fantatsic Beasts and Miss Perigrene among others have similar themes and allegories going on as X-men.
Bottom line is these characters are different, and different stories are to be told because of it. Can't replace Deadpool or Wolverine and they can't replace Cyclops, Rogue or Jean either. Again, the characters themselves are what gives X-Men their marketability, and that has been where Fox continues to drop the ball. Keep giving characters barely any lines or development, and new audiences will treat them as unimportant or audiences familiar will be disappointed.
What matters for both studios is how they portray said characters and if the script is any good. If Marvel got the X-Men themesleves right with a decent script, success will come from that.