There are a lot of questions there Lancer
And most of them, I am not qualified to answer. But they do prompt some thoughts about the nature of knowledge. I'll respond a little, mostly just to explore the ideas.
You are correct: space and time are bent. That is not a new concept. In fact, since Einstein, space and time have been considered inseparable. Hence the term 'space/time'.
Speculations about black holes can be extrapolated from our knowledge that a clock in space records a different 'speed' of time than a clock on the Earth's surface. In fact, it has been demonstrated that a clock at the top of a tower reads time at a different rate to one in the basement. That is another example of the value of developments in precision instrumentation.
The mass of an object bends space, in the same way a bowling ball creates a dip in the surface of a trampoline. The more mass, the more space/time is compressed. In astronomical terms, the Earth is not very dense (massive). Therefore the compression in space/time is comparatively small. Black holes are massive, therefore the compression in space/time is astounding.
I am already reaching beyond my ability to speak authoritatively on that subject. So I'll stop there.
I agree, a lot of ideas have changed. However, in astronomy, they tend to change in the same direction, not back and forth. Astronomers, and other scientists tend to be very conservative. Early astronomers were trying to find evidence for what they thought was a finite universe: the Earth was at the centre, there were nine celestial bodies, and then the sphere of the stars. As they collected better data and better mathematical methods, they learned that it was bigger than they thought. Eventually they realised the Sun was not at the centre of the universe, but rather, it was just one star among many. This had been hypothesized by philosophers such as Rene Descartes and Giordano Bruno. The latter was burned at the stake by the church for heresy.
The question of steady state, versus expanding universe was answered pretty well by the discoveries of the Hubble telescope, and calculations based on the red-shift of light travelling over distances. The universe is not only almost unimaginably big, it is also flying apart at an incredible speed.
Yes knowledge on the subject has changed, but as I mentioned earlier, the changes have always been in the same direction. The more we learn, the bigger it gets.