Arnold is one of the most powerful VFX/Film production renderers in the world. Not exactly designed to render a sphere on a plane, a more realistic showcase might be the space station scene from the film Elysium that it rendered. Try running that scene through Blender/Cycles.
It’s only now that it’s fully integrated into Max/Maya that it is enabled for GPU. CPU rendering in its native VFX/film environment is not a problem when you’re running a render farm with 1000s of cores.
I do my rendering in Max/Arnold and have recently started using 2.80. Cycles and the node editor is easy to use, but nowhere near as powerful as Arnold on more complex scenes with instances or displacement, with 1000s of objects and 10s of millions of polys, or complex and deep shader graphs.
2.80 is fantastic and I’m having a lot of fun learning/using, but(maybe this is a beta thing) the whole thing just falls apart with any kind of complex scene that Max/Maya wouldn’t even blink at.