Height and strength is required these days. Forget about it if you don't have it unless you have absolute supreme talent.
You didn't get me right. This guy (Kokkinakis) is taller and, than off-course, stronger. But Coric isn't small and weak, he is younger and should develope well.
Beside that, the best players are 185 (Sampras, Federer, Nadal). If you are too tall you can't be conistent from the back line which is the most important thing in today's tennis. Tsonga like players (like Kokkinakis is) can't rule the tennis nowdays.