Earlier quoted context omitted.
No, there have been numerous other signs of relativity, going all the way back to the unexpected aberration of the orbit of Mercury that Einstein was aware of. Eventually somebody would have noticed the gravitational deflection of the stars during eclipses, too, though it could have been decades before that happened. (Not because of technology, of course, which clearly existed in Einstein's day, though just barely, b…
That's for special relativity. I've read claims that if Einstein hadn't developed general relativity, we'd probably still be waiting for it.
Have you seen those string theorists? I'm not a big fan of string theory, but anyone who can even remotely navigate those things could work out GR in a few afternoons, with all the advantages another 100 years of evidence and developments would bring. (Sort of a weird thing to say since it's already worked out, but still.)
You think all those smart people would just be diddling around, going, gosh, I sure wish I could reconcile this overwhelming data that points at a 100+ year-old mathematical formalism, but I guess we'll just have to dick around for a while longer!?