Agree with some of this but I think the nature of the parties themselves (here and in the US) are much more to blame than the media or modern discourse.
To be a politician nowadays, especially a senior politician, requires someone to have started in their late teens. The vast majority of them (certainly in the UK) do not get the chance to achieve anything significant outside politics because demonstrable competence (or ability, or talent) isn't anything like as relevant as making connections, climbing up the ladder and ending up in a safe seat are. Even winning and losing elections are of secondary importance, as the panoply of support jobs (consultancies, think-tanks, commentary and other media roles, charity jobs (very well paid ironically) and public sector roles or peerages etc) are always available to the defeated.
This careerism is of course what results in the vicious opposition to anything that presents a threat to that existence, as we have seen with Corbyn and especially with AOC in the US - the mere fact they both did what they did is a threat to the whole system.