There isn’t a way to count how many sub fields have a specific value without looping over the repeater, or looping over something. A repeater will return a nested array of rows and you can loop over that.
$total = 0;
$repeater = get_field('repeater');
if ($repeater) {
foreach ($repeater as $row) {
if ($row['sub_field_name'] == 'the value your looking for') {
$total++;
}
}
}
echo $total,' rows of ',count($repeater),
' total rows have the value the value your looking for';