page.goto() already resolves to the main response:
const response = await page.goto('https://example.org/');
console.log(response.headers);
{ date: 'Sun, 29 Oct 2017 13:35:59 GMT', 'content-encoding': 'gzip', 'last-modified': 'Fri, 09 Aug 2013 23:54:35 GMT', server: 'ECS (lga/1318)',