The amount of cope is unbelievable.
Yes, it's based on a playboy bunny. Rabbits are a known sex symbol, even without Playboy's influence on them, due to their known hyperfertility.
However, Playboy rabbit suits aren't the only influence. The size, shape, and placement of the eyebrows are reminiscent of the jackalope.
The design also reflects its stats. Long legs on a slender physique help people realize Lopunny is a fast Pokemon and the guarded post with its arms to its chest helps key opponents into its otherwise surprising bulk.
Besides, it's not like "b-b-b-but sexy rabbit" is even the most sexual thing Pokemon has ever put into a Pokemon.