Rotten Tomatoes has every episode of the Season marked as 100% except for Charades which is notably not the musical episode. MetaCritics aggregate has the season at 81 overall. If you go to individual episodes there are only 10 reviews for Subspace Rhapsody. Most of them are positive. Two are negative, with one admitting that they didn’t even watch the episode and the other one responding with what sounded more like a tweet than a review. “OMG WHAT A HORRIBLE PIECE OF SHIT” does not a valid review make. Then there’s the fact that Subspace Rhapsody has gotten tons of acclaim and had tons of articles written about it in a positive light, much like the one you’re commenting on.
IMdB reviews are notoriously unreliable and using them as the sole rating system to say what you should and shouldn’t make? Not a great idea.