It was a great shot, but I think the first shot of the rack was the most impressive. I've seen a handful of sporty masse shots and 4-raileres on youtube (mostly by Efren), but I've never seen anyone pull off a timing shot like Melling did. Heck, out of all my years surfing pool vids on youtube, I can only recall one other video where someone even attempted a timing shot. It was Ortmann playing 8 ball and his attempt at a timing shot wasn't even close.
I agree with you that the timing shot is more rare, but I don't think the execution of the timing shot was as difficult as the execution of the masse. The masse was not a common masse where the cueball curves a little bit after getting around an object ball close to it--it required the cueball to curve dramtically, and with great precision, I'd say about five feet from the initial point of contact.
The timing shot did not require any kind of special stroke, whereas the masse required a 90 degree address of the cueball and a very big stroke to execute.