Not sure it is for me to respond - if that is their view so be it.
But we've seen this before - there were plenty on the hard left who wouldn't vote Labour while Blair was leader. Many of them left the party. But regardless of missing the votes of these supposed 'core' Labour voters Blair managed to win 3 elections each with either a landslide or a comfortable working majority. Point being, you win elections broadly from the centre ground, or certainly you need to be seen as the less extreme of the main parties. Hence Corbyn's problem and why I cannot see him winning an election, let alone a working majority.
Umunna has not put himself in the position where he could be leader of the opposition.
Not many from the section of the party which you argue would win labour the vote have been in that position since they absented themselves the field of frontline opposition politics en masse after the Referendum.
If we need a reminder of when and how the rats left what they thought was a sinking ship here is John Rentoul in the Independent at the time.
https://www.independent.co.uk/voices/labour-leadership-tom-watson-angela-eagle-lisa-nandy-keir-starmer-who-are-the-candidates-who-could-a7108186.htmlEven out of those who remained Kier, Tom and to some extent Yvette, who out of them has distinguished themselves as the next leader?
I myself was disappointed that Dan Jarvis didn't stand since his square jawed ex army practical Labour was I felt exactly what we needed against Cameronian chinless spinning.
Dan didn't get involved for perfectly laudable reasons but now three years later not only has one job but two jobs one of which at a pinch puts him on a Boris Johnson style Ark to the top Job. He is where Boris was eight years ago so now Dan is wholly inappropriate as the 2022 candidate.
Corbyn though turned out to be a phenomenon. First Garnering a membership Labour are not a dying party in terms of membership, secondly opening up a new constituency of voters, youth, thirdly saving the party by not resigning in 2016, Charismatically raising the vote for Labour at the 2017 election and overturning the tory majority and
finally in extrapolation of the vote of 2018 coming out as the party, which by coalition or confidence and supply or merely just not being able to stomach the tories, that would be in government.
If there are people that think Corbyn should not be leader....what are they doing about it? Since just getting Corbyn to resign and worrying about the rest after is not a solution.