They're not doing anything close to what ILM had to deal with on the movie. ILM had a much harder task, they had to composite the CGI into pre-shot, live action plates. Matching the lightning and the camera moves, not to mention translating the mocap data into usable animation, and heavy additional work on the facial stuff, reacting to live actors, and all authored at at least 4K resolution. The movie had a $150 million budget. This cinematic probably cost a few hundred grand at most.
It's true that it would probably take Blizzard's small team way too long to make an actual movie, but to try to compare them to a professional visual effects company is pretty ignorant. A more apt comparison would be with Pixar, and it's pretty obvious that Pixar could easily make a CGI movie of this quality.