製品IDでこの新しいメソッドを作成して呼び出します。また、adminで有効にする評価オプションが1つだけであることを確認してください。
public function getAllStart($pid) {
    $review = $this->_objectReview->getCollection()     //\Magento\Review\Model\Review $reviewFactory (_objectReview)
            ->addFieldToFilter('main_table.status_id', 1)
            ->addEntityFilter('product', $pid)          //$pid = > your current product ID
            ->addStoreFilter($this->_storeManager->getStore()->getId())
            ->addFieldToSelect('review_id')
    ;
    $review->getSelect()->columns('detail.detail_id')->joinInner(
            ['vote' => $review->getTable('rating_option_vote')], 'main_table.review_id = vote.review_id', array('review_value' => 'vote.value')
    );
    $review->getSelect()->order('review_value DESC');
    $review->getSelect()->columns('count(vote.vote_id) as total_vote')->group('review_value');
    for ($i = 5; $i >= 1; $i--) {
        $arrRatings[$i]['value'] = 0;
    }
    foreach ($review as $_result) {
        $arrRatings[$_result['review_value']]['value'] = $_result['total_vote'];
    }
    return $arrRatings;
    }