A speed of light has definitely been measured. We do it all the time. We measure radio waves in frequencies and we have even slowed down light to a relative snail’s pace. We even measure distances by the time it takes for a signal to reach another side through a medium like fiber optics or copper.
First mistake: the speed of light is variable depending on the medium it is traveling through
Second mistake: the theoretical maximum speed of the speed of light in a vacuum in a flat area of space has been empirically established
Third mistake: the speed of light is not a speed barrier - the speed of light has been increasing ever since the Universe popped into existence, if you were an observer outside the Universe that is the speed of light has been increasing and at some point spacetime expansion will go faster than the speed of light. the speed of light can be a lot faster than the speed of light, information cannot travel faster than the speed of light. For example if you point a laser at the moon and then move that laser pointer very quickly back and forth, the laser, when viewed on the moon will appear to go back and forth faster than the speed of light, obviously with this method no information is being transferred to the moon any faster than the speed of light.