I don't even recall what we are debating anymore, but we have no exact figures for the Hydralisk's height, except for the back of the original box.

Cinematics don't do scaling well anyway. Compare the sizes of the battlecruisers in "The Inauguration" compared to the Brood War introduction.

"In the book Starcraft: Queen of Blades by Aaron Rosenberg, Raynor described the protoss as about 7 feet tall which is about 2.1 meters."

By this wiki's canon policy, the game trumps novels. (Also, in Firstborn, a nearly seven-foot tall man is considered short by the Protoss.)

"And in Starcraft II, the ultralisk is at least 13 meters tall."

Where did that come from? I'll be happy to put that up with a source. (Note that the game itself doesn't get referenced as a source. For instance, you don't have to source that Vultures do 20 concussive damage as you get that from the game. That's why there's no "back of box" reference for Protoss height; that's part of the game.)

"But aren't hydralisks taller than protoss?"

I don't believe we've seen videos of Hydralisks vs Protoss, except once, and even then you can't tell their actual measurements from the video. (There are websites devoted to Star Trek, Star Wars and Babylon 5 that do those kinds of measurements, but they're done by professional engineers who show their work, and their answers are always like "it's 50-75 meters" due to variance.)