It was my experience, turning 18 in 1980, that Polys were a highly valued part of the HE landscape.
Yes, they were often only marginally easier to get into than unis, but they tended to err towards more higher level vocational subjects, often with that important sandwich year in industry.
But the UK is not alone in falling into that 'uni for all' (but because obviously a lot of kids aren't quite academic enough for actual uni, we'll rename their colleges to give the illusion of suddenly academically smarter kids); hence Queensland Institute of Technology is now Queensland University of Technology.
And, in doing so, we now turn up our noses at anything that doesn't have the word 'uni' in it.
FTR, I bet Southampton Solent is in trouble....