Completely agree. It's a textbook example of hindsight bias when people cannot "unsee" the currently accepted theory deemed to be "true" and fail to imagine that people in the past thought just like them before the new theory came along. I think it takes a good amount of marketing (eg. Einstein with Relativity) to change people's mind if a new improved theory is to be accepted and for majority to conform to it.
So let's indeed be very charitable in crediting our predecessors' achievements.
What do you mean by marketing? Einstein didn't need much convincing, as he proposed experiments that would falsify or confirm general relativity. The theory is also not only mathematically sound but very elegant. Acutally, Hilbert arrived at the same equations using a competely different, more mathematical approach using the least action principle, which is another good sign it was correct. But the smoking gun was of course Edison's observation of gravitational lensing during an eclipse.
But of course the topic in this subthread is special relativity. And I think the speed of light being constant and a maximum speed is one of the most fundamental and most assured fact about the universe that we know, because it's more than just some speed of some particle. It's a geometric property of spacetime, a Lorentzian manifold. I doubt it will ever be looked upon as some sort of horrible blunder, just like no one ever thinks less of Newton just because he only found an approximately correct theory. I think it's foolish to doubt it just to be contrarian.
Could it be wrong? Sure, we look for violations of Lorentz invariance all the time. But the boundaries we have on it are extremely good. But if someone claims to have observed superluminal speeds, I'll doubt the experimenters more than I'll doubt special relativity, because of the strong priors we have on it. This happened by the way a few years ago, where some Italian lab claimed to have seen superluminal neutrinos. Most professional physicists didn't believe it. It turned out to be a faulty cable.
> the smoking gun was of course Edison's observation of gravitational lensing during an eclipse
Actually, the fact that Eddington's (not Edison's) eclipse observations were treated as a "smoking gun" was an example of marketing, since we now know that Eddington's actual data was simply not good enough to resolve the effect in question (bending of light by the Sun). The reason the claimed result was accepted without question was Eddington's prestige, i.e., marketing. If it had been someone with less prestige the results might have been examined more critically.
and while maybe you could say it was about gravitational lensing, the observatories (and Earth) was so far from any possible caustic that it's better to leave it at just deflection of light.
So let's indeed be very charitable in crediting our predecessors' achievements.