A simple question, is the speed of light the same in any direction measured on the surface of the Earth ? If yes then Sagnac effect does not exist, if no then Relativity doesn't exist.

Anyway the Theory of Relativity has very little importance because has a very small use and in electronics has no use at all. You don't need Realtivity for television, cell phones, computers, comunications, robots, etc, etc, etc

Stupidity also evolves!