My feeling is that accents have become much more accentuated in recent decades - certainly in urban areas. It is as if accent has become a badge of identity amongst certain demographics. In London, even many young white people speak with a black ‘street' accent, for example; and ‘estuary’ english spread out into the home counties quite some time ago. I also think popular soap operas have spread certain local dialectical words into the broader population. For example, I’m pretty sure, “ It’s all kicking off...” originated in Liverpool - and spread with the popularity of Brookside.
You mention that harsh type of Liverpool accent above, and I’d agree it is not very pleasant. The roots of the Liverpool accent originate in a combination of Lancastrian, Irish and Welsh sounds and inflections. Growing up in Liverpool I was not aware of anyone speaking in that harsh, exaggerated way, though - it was always a lot softer. Most of the adults I knew sounded more like the Beatles than Paul O’Grady ( he’s from Birkenhead; but then so is Paul Hollywood and his accent is not so harsh).
My family moved down to Buckinghamshire in the early 1980s, when I was 16, and people would ask me where I was from; “ somewhere up North, or maybe Ireland”. People had the image of people running between each others' terraced houses, borrowing cups of sugar.
Over the years I’ve lived in different areas of the country - and when living in Scotland I was often acutely aware that my accent was ‘English’. This was often uncomfortable. I’d feel I was part of the oppressive colonial force. My husband’s family all speak with ‘posh' southern accents; very middle class - and I’ve always been aware of my ‘difference' in family & social situations. But then coming back up to Liverpool my accent is seen as being posh by some.
There is definitely prejudice against regional accents & dialects, with people speaking with them being perceived as being of lower social status; although some accents - soft Irish and Scottish accents do not carry this stigma.
To my ear I can’t really tell the difference between the various ‘northern’ accents ( except for Geordie), including the various Mancunian accents and Leeds/Yorkshire accents. They all sound like a continuum of the same sort of sound. And sometimes even mild Manchester accents can sound like a mild Liverpool accent to my ear.
When living elsewhere, I’d always get a warm feel on hearing a soft Liverpool accent on the phone. Friendly and familiar.