Unless I’m misunderstanding, IMO a nested array_map would be the way to go. IIRC ACF repeater fields just return an array, so it should be as simple as this:
public function propertyLoop() {
return array_map(function ($post) {
return [
'bathrooms' => get_field('property_bathrooms', $post),
'sleeps' => get_field('property_sleeps', $post),
'bedrooms' => get_field('property_bedrooms', $post),
'title' => apply_filters('the_title', $post->post_title),
'introduction' => get_field('property_introduction'),
'link' => get_permalink($post->ID),
'gallery' => array_map(function($image) {
return wp_get_attachment_image($image); // Or however you want to process this
}, get_field('property_gallery', $post)),
];
}, get_posts([ 'post_type' => 'property', 'posts_per_page'=> -1, ]));
}