Terrific question ... profound ... your post can actually becomes someones PhD research.
First, to answer your questions:
(1) Yes, people did actually enjoy watching public deaths and torture -or, at a minimum, at least the people who attended such events did.
(2) Yes, our minds have changed with evolution ... however, on a planet with 6.7 billion people and where many (estimated in excess of 50%) are considered living in poverty, it can be inferred that evolution (and, thereby, our mind) has not engendered a fair and equitable shift for all ... in fact, evolution has been quite picky and discriminatory (but then, I believe that's what evolution does remarkably well).
(3) I'm not certain if "horror movies" today are an acceptable form -or replacement- for the "live" acts of our predecessors, but it must be understood that horror movies, gratuitous violence, rape, murder, destruction of people and property as depicted in our movies -and written works- does have an audience and, arguably, an influence.
The question for researchers (from neuro-scientists to sociologists, from anthropologists to psychologists ... and everyone in between) is "what actually differentiates a person who not only watches but possibly enjoys [derives some pleasure] the blood, mayhem, and denigrating of other humans versus someone [like you] who says, 'I don't enjoy watching others suffer'?"
Depending on the sources anyone who choose to read and assess, it seems likely there are multiple approaches to attempting an answer to your fascinating question. For me, I tend to rely more on the cognitive and biological imperative of our human nature and look for clues and evidence via our brain.
Briefly, there seems to be a peculiar relationship between our species' urges for pleasure as well as violence. Indeed, throughout history, there is evidence of overt sexual pleasure deriving from horrific acts on others -to the point that a need for sexual gratification seemed to drive the propensity to engage in violence. With that said, not everyone is violent and not everyone derives their pleasure via a violent predisposition.
That, in my view, leads to a brain-based pleasure center as well as violence center and, for each of us, our hardwiring comes with both but for reasons not yet understood, some are prone to a violence personality while others to a pleasure personality.
So I'm not misunderstood in my assertion, please know that I'm not constructing a "good versus bad" dynamic but more of a continuum where all human tendencies can -at a minimum- be placed and reviewed for analysis and interpretation.
(4) I do believe our ancestors were more violent in nature -because evolution demanded that- and that today, relatively speaking, more people are at -or desire to be at- peace with one another than killing one another. Nature has tweaked the environment as well as evolution has tweaked our species. It's possible that those who derive some pleasure from watching horror movies, torture, death and destruction, etc. simply have a violence center that continues to outweigh their pleasure center.
Once again -terrific question!