I must have snooty written all over me - but then again I am a rhyming snob. For me perfect rhyming falls over when the writer doesn't really understand the correct meaning or syntax of the word. That's often the case with songs written/sung in English by non native speakers: Abba were the most famous though not always most obvious exponents of this. Not always the case though - & becoming less so. It's has also become more common with native speakers who raid rhyming dictionaries with only a glance at the Pocket Collins afterward or when Lou Reed rhymes vial & vile.
Sweeny Todd is great writing - and the cube performance from the mid 80's was it's peak for me.