So much wrong in this untutored diatribe. Where to begin? It's difficult because it mostly relies on simplistic empty pejoratives like 'hard left' and 'Leninism'. On the question of Brexit, the non-monetarist section of the Labour Party was always Eurosceptic. Maybe you're just not that observant? Or just too young to remember or too lazy to check? In that respect Corbyn's position maintained absolutely a consistent position. As did Dennis Skinner, whatever anyone may think of their view. No doubt this did not chime with the New Labour contingent and their gaggle of economically clueless (and historically clueless) supporters. Hardly surprising.
The fact a left party doesn't gain traction in British elections is not an argument against rightness/wrongness, truth/falsity of their view or position, but as always in elections on who can better 'persuade'. Or in clearer terms: whose propaganda is best. And since right-wing propaganda appeals in a broad way to emotional and simplistic views far better (and has better funding), we have what we have.
You clearly have understood nothing in appointing yourself a cheerleader for the economically impotent centre-left. You think Blair and co gained 'power' by merely shifting itself away from 'the hard left' into so-called practical modernisation? Think again. He merely made friends with the holders of actual power and influence by conceding political power. Dinner with Rupert Murdoch got him to be championed by The Sun. Concession to corporate Britain got him to be supported by corporate Britain. What you got with New Labour is a party that gained office, but not power. And office for whom? Very big difference there amigo, upon which you might like to ponder for a while.
I realise the far left (better?) continue to struggle in the UK and are now, arguably, irrelevant to political debate in 2021. This is largely down to voter preferences, the effectiveness of the Tories and JC's tenure - he did more to undermine the left (and Labour in general) than anyone. So be it. But what of the far left abroad. There too things aren't going that well - for example, Venezuela (MMT fans, and fondly spoken of by Corbyn). Like other far left countries, it can't seem to operate without a big dollop of totalitarianism. And why for all the glory of far left economic policy is it that the common Venezuelan man (and woman and child) is suffering the most. It's a shame as the country is blessed with natural resources. There is China of course, a sort of hybrid of capitalism and communism - but they seem to be doubling down on the Communism part. And Xi is no democrat.
Re: your post: it seems you have taken hard left and Leninism, and my post in general for that matter, personally - and reacted accordingly, but briefly...re: JC - he is and always was a EU-skeptic, and was inconsistent in his position during the referendum. The far left really need to understand the electorate more fully and talk to voters more often, especially the ones they don't like (inclusion and national conversations, etc) if they want to get into No.10. Generally in democracies, the losing party (with its manifesto) realise they have taken a misstep and change their course, message and manifesto. It makes sense. I did see the BBC programme on Blair/Labour/Murdoch a while back - very interesting and well worth watching.