So the result should be the following?

  "aggregateRating": {
    "@type": "AggregateRating",
    "ratingValue": "<?php echo osc_count_item_comments_rating() > 0 ? osc_count_item_comments_rating() : 5 ?>",
    "bestRating": "5",
    "worstRating": "0",
    "ratingCount": "<?php echo (osc_count_item_comments() > 0 ? osc_count_item_comments() : 1); ?>",
    "reviewCount": "<?php echo (osc_count_item_comments() > 0 ? osc_count_item_comments() : 1); ?>"
  }

Yes but you want to use rating vslue instead of count.
Woukd say you've provided wrong code at start.

But that's the original code. I didn't touch anything. So it is valid or something is wrong with it?