There's too much time spent arguing about left, far left, right, far right, blah blah blah. Nobody cares aside from a small bubble of political anoraks. Most Americans are thoroughly innocent of ideology. The way they vote is determined by their social context. They don't like policies that are marketed as far left, not because they dislike those policies, but because most Americans are deeply apolitical. Having an ideology - a coherent, fully formed jdeology - is pretty weird. By calling yourself far left, you're saying something like: I'm not like you. People won't vote for that.
But actual policies? People don't really pay any attention to those. So if you want to win, get whatever set of policies you like, and then figure out why people might want them. Most Americans like leftwing policies when presented in the abstract... but not for the reasons liberals like them. Liberals tend to have expansive, universalist notions: we ought to provide anyone healthcare on principle. The average American has, and is perfectly normal in having, tight, communal notions: I'd hate it if my sister fell ill, she should be cared for. I grew up with these guys, they're just like me, and now they don't have a job: someone should do something. But you can't just apply that to someone outside their bubble, because these leftwing notions are based on small-c conservative, almost familial principles. They don't apply to people you don't know and communities you don't understand. And it definitely isn't a valid response retreat into being some kind of bland, anodyne centrist, because people don't identify with them any more either. The technocrats are dead.
The Labour Party's problem is that neither side really gets it. Corbyn's busy trying to be the most socialist socialist ever to socialist, and selling up his far leftiness every three seconds. Meanwhile, Kendall and co. are just offering Blair tributes in an era where Blair is an even more unpopular politician than Corbyn - it's not 1997 any more, times change. It's just frustrating seeing the Democrats doing the same thing, with a time lag of about nine months. No, going super hardcore far left with your marketing isn't going to work. At the same time, trying to embrace liberal technocracy won't either.