similar looking aircraft
Thanks to the laws of aerodynamics and materials science, there are only so many ways you can lay out an aircraft performing any given role.
There's not much difference to the casual observer between most fighters in any given size, whether french, american russian, european or chinese, in the same way that apart from styling there's virtually no difference between most cars of any given size on the road.
Some of the chinese designs are more adventurous than western or russian versions (one example being the box wing on their drones, which gives greater performance at 60,000 feet). Everyone spies on everyone and it's overly simplistic to write china off as copycats.