There's a famous study that concluded "CEO effects" only account for about 14.5% of performance [1]. It may be quite dated by today, though, it may be even less pronounced according to [2] that claims more recent studies show the CEO only explains for 4.5%-12.8% of performance.[2]

[1] https://www.jstor.org/stable/2094020?seq=1

[2] https://www.theatlantic.com/magazine/archive/2009/06/do-ceos...