The Principle is good, and so is their longer one Journey to the Center of the Universe. One can learn much from their perusal (and animations!) of the ether drift experiments and the imposition of relativity, but they also avoid that which counters their hypothesis, such as data indicating the CMB is caused by Earth's water content and is not a remnant of some mythical Big Bang. I respect their work but don't agree with their conclusions.

Watch the video I posted here, it shows a buoyancy experiment on a plane performing a microgravity maneuver which directly counters your claim. While gravity can't be explained its effects can definitely can be calculated and engineered, claiming it doesn't exist because the theory isn't proven is a logical fallacy.

https://steemit.com/flatearth/@alkemix/super-ultimate-flat-earth-debunkification

Curvature is measured and seen daily, even thought the flat earth hypno-vids keep claiming the opposite. Check all your facts before making claims!