Your question is very broad so I cannot answer all of it. At the general level I would take issue with your premise. Most people, for most of recorded history, so far as we can tell have viewed history as a decline. They broadly believe the world they live in is not as good as the world their parents lived in and that some prior time was a 'golden age'. You can see this in newspapers and political movements anywhere you look today. Obviously that is not true but it is a sentiment that is widely expressed and therefore presumably widely believed. The exceptions are obviously exceptional - the Roman Empire under Augustus, parts of the nineteenth century in Europe, perhaps the 1960s.

Very broad musings aside I can give you two very specific Indian examples. Embedded within texts from India called the puranas (it means 'old'), which are mostly religious, are copies of a dynastic listing presented as a prophecy, probably written in the fourth/fifth century AD. For this I will quote from Pargiter, F.E. (1913) The Puranic Text of the Dynasties of the Kali Age. At the end of the list of kings the text swings off into an assessment of current woes, and the following is what we find:

“There will be Yavanas here by reason of religious feeling or ambition or plunder; they will not be kings solemnly anointed, but will follow evil customs by reason of the corruption of the age. Massacring women and children and killing one another, kings will enjoy the earth at the end of the Kali age. Kings of continual upstart races, falling as soon as they arise, will exist in succession through Fate. They will be destitute of righteousness, affection, and wealth. Mingled with them will be Arya and Mleccha folk everywhere: they prevail in turn; the population will perish.”

Yavana and Mleccha are (roughly) terms for foreigners. So this is real moral panic stuff - all our politicians are corrupt, everything is bad because of foreigners, and all is collapsing. Very much framed by an idea that all was better in the past (again, this is a written as a prophecy).

This is not the only prophecy which shows a similar view that things are terrible. In the Buddhist community (samgha) there are a lot of prophecies that suggest that the samgha will collapse due to corruption, infighting, and the evils of the world. They are generally framed as suggesting this will happen five hundred years after the death of the Buddha. And of course since it is easier to write an accurate prophecy after things have happened we can assume these texts were mostly written in the first and second century AD (about five hundred years after the Buddha). So these are a few centuries earlier than the puranic texts and they show a similar idea that things are on a downward path from a much better past (in this case the idealised period of the Buddha's life). This group of prophecies is discussed in Nattier, J. (1991) Once upon a Future Time: Studies in a Buddhist Prophecy of Decline, which I have not read but have wanted to get to for a long time.

Now these are just two examples, but my feeling is that if I went to the various chronicles I have and started working through them most would exhibit the same general framing, that the exceptions would be rare. And, of course, as I said at the beginning this is clearly wrong, any cursory knowledge of history tells you it is wrong, but it seems to be a very common way in which people frame their own time, and I don't think it is specific to any period or place, I think it is a cross-cultural phenomena that has something to do with how human being experience the world in which they live. It is something I've always had an interest in but obviously the practicalities of studying anything on that scale are daunting and I have never had the opportunity to pursue it.