Good analysis. I too think London Road is pretty good, a 'proper' vibrant city street. A city can't be all twee little pedestrianised walkways and expensive boutiques, although there is a place for them as well - and Brighton has them.The answer is that it's getting better in some ways and worse in others.
Worse: the vandalism, the tagging, the expense of housing, the influx of Londoners, the crumbling Arches, the empty shops, the ridiculous i360, the crime, the potholes, La Cappanina has closed, still bugger all happening at Black Rock, too many student properties, the Manhattanisation of Lewes Road.
Better: the North Laine, the explosion of decent places to eat and drink, especially at beach level along the seafront, Albion shirts everywhere, the sheer vibrancy of streets such as London Road and Lewes Road that were once drab and down-at-heel, the new hospital building, the Amex, Albion in the Premier League.
It could be better, but it's still one of the best places to live in the UK.
Ditto Lewes Road up to the Gyratory, then when it gets into the Education Quarter as you say it gets a bit bleak and functional, although I think the architecture is pretty good.