As is starkly shown
here, the style of the towers and wall is very similar to the famous Alan Lee illustration. I would be surprised, therefore, if Lee was not invvolved in the design of the Gate, and Howe too, given that they were working together.
Personally, I don't care about the physics or other practicalities of such matters. I just care whether it looks good. And it looks good to me (yes, including the Trolls).
