Momentum only helped friendly candidates
Rather than helping the party as a whole, Momentum acted as a party within a party, only lending assistance to candidates aligned with its ideology.
The big-name strategists that managed to guide Labour to its strong 2017 election performance were missing from the 2019 election.
Labour lost many of the strategists that had guided the party to its near-miss in 2017. Those that replaced them were inexperienced and not up to the task of running a national election campaign.
Karie Murphy took over the coordination of Labour’s 2019 general election campaign. She swiftly adopted a strategy of 99%. Instead of channelling resources to the marginal and winnable seats, as well as shoring up its heartlands in the north of England, Murphy opted to spread resources across the country and challenge Tory seats in 99% of constituencies. This was an error and only served to highlight her inexperience. Right from the off, Murphy told party insiders she was going to ignore polls and conventional campaign strategy. Her refusal to look at data was a colossal error that would ultimately cost the Labour Party dearly.
Enter the counter arguments here ...
[P1] The steady hands that masterminded Labour's strong 2017 election showing were absent in 2019. [P2] Those that replaced them were inexperienced and couldn't run an effective national campaign strategy. [P3] This was behind Labour's disastrous 2019 election performance.
Enter the technical rejections of the premises here ...