leadership does affect the election outcome

• Tony Blair: 'The Labour Party leader's high approval ratings propelled Labour to big election wins in 1997 and 2001, but Blair's waning popularity after the Iraq War correlates to Labour's reduced majority after the 2005 general election.'
• Jeremy Corbyn: 'A 2019 survey of former Labour voters found that 43% of respondents cast their vote on the basis of 'leadership', perhaps highlighting how dislike of Corbyn helped shatter the so-called 'red wall', former Labour-held safe seats that were won by the Conservatives.'